Electrostatic copying apparatus

ABSTRACT

An electrostatic copying apparatus comprising a lower supporting frame, an upper supporting frame mounted on the lower supporting frame for pivotal movement between an open position and a closed position, a document placing means having a transparent plate for placing a document to be copied thereon, an optical unit and a driving source. Either the document placing means or at least a part of the optical unit is mounted reciprocally on the upper supporting frame and drivingly coupled to the driving source via a power transmission mechanism. The apparatus further includes an automatic locking means for automatically locking the document placing means or at least a part of the optical unit and cancelling the locking according to an operation of moving the upper supporting frame to an open or closed position or an operation incident to this moving operation.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a division of application Ser. No. 596,121, filedApr. 3, 1984, now U.S. Pat. No. 4,636,057.

FIELD OF THE INVENTION

This invention relates to some improvements in an electrostatic copyingapparatus.

DESCRIPTION OF THE PRIOR ART

Electrostatic copying apparatuses of the so-called shell type includinga lower supporting frame and an upper supporting frame mounted for freepivotal movement between an open position and a closed position havebeen proposed and come into practical application. Generally, in such ashell-type electrostatic copying apparatus, when the upper supportingframe is held at the open position, at least a considerable portion of aconveying passage for a sheet material such as a copying paper isopened. Hence, if jamming of the sheet material should occur in theconveying passage, it can be easily taken out. However, the conventionalshell-type electrostatic copying apparatuses have certain problems to besolved.

(i) For example, when the upper supporting frame is to be brought fromthe closed position to the open position, it is important toautomatically hamper the free movement of a document placing means or atleast a part of an optical unit mounted reciprocally on the uppersupporting frame incident to the movement of the upper supporting frameto the open position. This requirement, however, has not been fullyaccurately met, or complex and expensive means are required in order tofulfil such a requirement fully accurately.

Electrostatic copying apparatuses, not limited to the shell-type,generally include a developing device for applying toner particles to alatent electrostatic image and developing it to a toner image, a fixingdevice for fixing the toner image on a sheet material, and in a type inwhich the document placing means is adapted to be moved at the time ofthe copying cycle, control means for moving the document placing meansin the required manner. Conventional electrostatic copying apparatusesalso have the following problems with regard to such devices and means.

A developing device of the type in which a so-called two-componentdeveloper composed of carrier particles and toner particles has beenwidely used in practice as the aforesaid developing device. Such a typeof developing device has the following problems.

(ii) In order to maintain the ratio between the carrier particles andthe toner particles in the developer at a certain required value bysupplying the toner particles as the toner particles are consumed, it isimportant to control the supplying of the toner particles by detecting acharacteristic of the developer corresponding to the aforesaid ratio,for example its inductance. However, depending upon the detectingposition, etc., the characteristic of the developer cannot always beproperly detected.

(iii) It is desired to mix the developer fully and make it sufficientlyuniform also in the widthwise direction of the developing device. Butthis desire cannot be fully achieved.

(iv) Generally, the supplying of the toner particles is controlled byproperly rotating a toner particle feed roller on the basis of thecharacteristic of the developer. But control means for properly rotatingthe toner particle feed roller is comparatively complex and expensive.

A fixing device including an upper and a lower roller cooperating witheach other and an electrical heating element disposed in at least one ofthese rollers has been widely used as the aforesaid fixing device. Thisconventional fixing device has the following problems.

(v) It is desired to vary the state of feeding of a sheet materialbearing a toner image to the upper and lower rollers depending upon thenature of the sheet material, for example upon whether it is relativelylight and has relatively low stiffness as in an ordinary copying paperor whether it is relatively heavy and has relatively high stiffness asin an official postal card. This desire cannot be fully achieved.

(vi) In the conventional electrostatic copying apparatuses equipped withthe aforesaid fixing device, various measures for saving powerconsumption are taken in relation to the temperature of the fixingdevice ascribable to the action of the electrical heating element, andthe performance or non-performance of the copying cycle. But suchmeasures have not proved to be entirely satisfactory.

(vii) As regards the control means for controlling the document placingmeans in the required manner, especially the one which is equipped witha microprocessor, the cost of production could still be reduced bydecreasing the number of required elements of the microprocessor.

SUMMARY OF THE INVENTION

It is a first object of this invention to provide an electrostaticcopying apparatus of the shell type which includes a relatively simpleand inexpensive automatic locking means for accurately hampering themovement of a document placing means or at least a part of an opticalunit mounted reciprocally on an upper supporting frame when the uppersupporting frame is moved from its closed position to its open position.

A second object of the invention is to provide a latent electrostaticimage developing device in which the characteristic of a developer canbe fully properly detected without adverse effects on the developingaction, etc.

A third object of this invention is to provide a latent electrostaticimage developing device in which a developer is fully mixed and madeuniform also in the widthwise direction of the developing device.

A fourth object of this invention is to provide a latent electrostaticimage developing device which is provided with a simple and inexpensivecontrol means for properly rotating a toner particle supplying roller.

A fifth object of this invention is to provide a fixing device in whichthe state of feeding of a sheet material bearing a toner image to bedeveloped to an upper and a lower roller is varied automatically in therequired manner according to the characteristic of the sheet material.

A sixth object of this invention is to provide an electrostatic copyingapparatus which permits saving of power consumption based on thetemperature of a fixing device and the performance or non-performance ofthe copying cycle.

A seventh object of this invention is to provide an electrostaticcopying apparatus in which the number of required elements of a controlmeans for controlling the movement of a document placing means in therequired manner, and therefore the cost of production, can be reduced.

Other objects of this invention will become apparent from the followingdescription.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified longitudinal sectional view showing oneembodiment of the electrostatic copying apparatus constructed inaccordance with this invention;

FIG. 2 is a simplified cross sectional view of the electrostatic copyingapparatus of FIG. 1;

FIG. 3 is a simplified view showing a driving system of the electostaticcopying apparatus of FIG. 1;

FIG. 4 is a simplified view showing a part of the driving system of FIG.3;

FIG. 5 is a simplified cross sectional view, similar to FIG. 2, showinga modified example of an automatic locking means for a document placingmeans;

FIG. 6 is a block diagram showing another modified example of theautomatic locking means for the document placing means;

FIG. 7 is a sectional view showing a developing device in theelectrostatic copying apparatus of FIG. 1;

FIG. 8 is a perspective view, partly broken away, of a rotary stirringmechanism and a partitioning plate of the developing device of FIG. 7;

FIG. 9 is a top plan view of a part of the partitioning plate and therotary sirring mechanism of the developing device of FIG. 7;

FIG. 10 is a rear view of the developing device of FIG. 7;

FIG. 11 is an exploded perspective view showing some constituentelements of means for controlling a toner particle supplying roller usedin the developing device of FIG. 7;

FIG. 12 is a sectional view showing the vicinity of a fixing device;

FIG. 13 is a perspective view showing a guide member;

FIG. 14 is a sectional view showing the state in which a sheet materialhaving relatively high stiffness is used;

FIG. 15 is a circuit diagram showing a part of a control system for theelectrostatic copying apparatus of FIG. 1;

FIG. 16 is a graph showing the relation between the temperature detectedby a thermistor and the time;

FIG. 17 is a graph showing the relation between the temperature detectedby a thermistor and the time in a modified example;

FIG. 18 is a simplified side elevation of a detecting switch provided inrelation to a document placing means;

FIG. 19 is a simplified top plan view of the detecting switch shown inFIG. 18;

FIGS. 20 and 21 are a partial sectional view and a partical sideelevation of constituent elements relating to means for detecting theamount of driving;

FIG. 22 is a block diagram showing elements relating to the controllingof the action of the electrostatic copying apparatus of FIG. 1; and

FIGS. 23-A and 23-B are flow charts showing the mode of controlling theaction of the electrostatic copying apparatus of FIG. 1.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS Outline of the CopyingApparatus as a Whole

The entire structure of one embodiment of the electrostatic copyingapparatus which has been improved in various respects in accordance withthis invention will first be described.

With reference to FIG. 1, the illustrated copying apparatus has a nearlyrectangular parallelpipedal housing shown generally at 2. The housing 2is defined by a lower supporting frame 4 and an upper supporting frame6. With reference to FIG. 2 together with FIG. 1, the lower supportingframe includes a vertical front base plate 8 and a vertical rear baseplate 10 disposed with a predetermined distance therebetween in thefront-rear direction (a direction perpendicular to the sheet surface inFIG. 1, and the left-right direction in FIG. 2), and a bottom plate 12fixed to the lower ends of these plates. The bottom plate 12 has abottom wall portion 14 defining the bottom surface of the housing 2 andlower surface wall portions 16 and 18 defining the nearly lower halfportions of the two side surfaces of the housing 2. On the other hand,the upper supporting frame 6 includes a vertical front base plate 20 anda vertical rear base plate 22 disposed with a predetermined distancetherebetween in the front-rear direction and a top plate 24 fixed to theupper ends of these plates. The top plate 24 has a top wall portion 26defining the top surface of the housing 2 and upper surface wallportions 28 and 30 defining the nearly upper half portions of the twoside surfaces of the housing 2. The upper supporting frame 6 is mountedon the lower supporting frame 4 so that it can pivot freely between aclosed position shown by solid lines in FIGS. 1 and 2 and an openposition shown by two-dot chain lines in FIGS. 1 and 2. Morespecifically, upwardly extending supporting projections 32 are providedat the right end portions of the vertical front base plate 8 and thevertical rear base plate 10 of the lower supporting frame 4, and thevertical front base plate 20 and the vertical rear base plate 22 of theupper supporting frame 6 are pivotally mounted on these supportingprojections 32 through a shaft 34. Normally, the upper supporting frame6 is locked in the closed position shown by the solid lines in FIGS. 1and 2 by a suitable locking mechanism (not shown), but as required, canbe pivoted to the open position shown by the two-dot chain lines inFIGS. 1 and 2 with the shaft 34 as a center by cancelling the lockingaction of the locking mechanism.

In the illustrated copying apparatus, there are also provided a frontcover 36 covering the front surface of the housing 2 and a rear cover 38for covering the rear surface of the housing 2, as shown in FIG. 2. Thefront cover 36 is comprised of a lower front cover 40 fixed to the lowersupporting frame 4 and an upper front cover 42 fixed to the uppersupporting frame 6. Likewise, the rear cover 38 is comprised of a lowerrear cover 44 fixed to the lower supporting frame 4 and an upper rearcover 46 fixed to the upper supporting frame 6. Accordingly, when theupper supporting frame 6 is moved from the closed position to the openposition, approximately the upper half portions of the front cover 36and the rear cover 38, i.e. the upper front cover 42 and the upper rearcover 46, can be moved to the open position in the same way.

A document placing means shown generally at 48 is disposed on the topsurface of the housing 2 so that it can reciprocate freely in theleft-right direction in FIG. 1 or a direction perpendicular to the sheetsurface in FIG. 2. As clearly shown in FIG. 2, the document placingmeans 48 which may be in a form known per se includes a supporting baseplate 50, a transparent plate 52 fixed to the supporting base plate 50,and a document cover 54 (omitted in FIG. 1) whose rear edge (left edgein FIG. 2) is pivotably mounted on the supporting base plate 50 by asuitably mechanism (not shown). With reference to FIG. 2, the method ofmounting the document placing means 48 will be described. A supportingmember 58 having a horizontal portion 56 is fixed to the rear surface ofthe vertical rear base plate 22 of the upper supporting frame 6, andbetween the horizontal portion 56 of the supporting member 58 and thesupporting base plate 50 of the document placing means 48 is interposeda sliding mechanism 60 (which may conveniently be one commerciallyavailable under the tradename "Aculide") extending in the reciprocatingdirection of the document placing means 48. On the other hand, a guidemember 62 having a rearwardly opened guide groove at its upper portionextending upwardly beyond the top surface of the housing 2 is fixed tothe front surface of the vertical front base plate 20 of the uppersupporting frame 6. The front edge portion of the transparent plate 52of the document placing means 48 is slidably received in the guidegroove of the guide member 62. Thus, the document placing means 48 ismounted such that it can freely reciprocate between a start-of-scanposition shown by a two-dot chain line 48A in FIG. 1 and a scan movementlimit position shown by a two-dot chain line 48B in FIG. 1.

With reference to FIG. 1, a rotating drum 64 having a photosensitivemember on its peripheral surface is rotatably mounted nearly centrallywithin the housing 2. Around the rotating drum 64 adapted to be rotatedin the direction of an arrow 66 are disposed a charging corona dischargedevice 68, an optical unit 70, a latent electrostatic image developingdevice 72, a transferring corona discharge device 74, a peeling coronadischarge device 76, a cleaning device 80 having a cleaning blade 78 anda charge eliminating lamp 82 in this sequence in the rotating directionof the drum 64. In relation to the optical unit 70, a documentilluminating lamp 84 is also provided. The document illuminating lamp 84illuminates a document (not shown) to be copied, placed on thetransparent plate 52 of the document placing means 48, through anopening 86 formed at the top wall portion 26 of the top plate 24. Theoptical unit 70 is constructed by arranging many elongate opticalelements extending in the vertical direction (for example, rod-likelenses sold under the tradename "Selfox Microlense" by Nippon SheetGlass Co., Ltd.), and as shown by an arrow in FIG. 1, projects thereflected light from the document onto the peripheral surface of therotating drum 64.

A sheet material conveying device shown generally at 88 is disposed inthe nearly lower half portion of the housing 2. At one end (the rightend in FIG. 1) of the sheet material conveying device 88 are provided acassette-type copying paper feed device 90 and a manual sheet feeddevice 92. The copying paper feed device 90 consists of a combination ofa paper cassette receiving section 96 having a feed roller 94 providedtherein and a paper cassette 100 to be loaded in the paper cassettereceiving section 96 through an opening 98 formed on the right sidesurface of the housing 2 (more specifically the right side lower surfacewall portion 16 of the bottom plate 12), and feeds copying paper sheetsone by one from a copying sheet layer 102 accommodated in the cassette100 by the action of the feed roller 94. The manual feed device 92includes a guide plate 106 protruding outwardly through an opening 104formed in the right side surface of the housing 2, a guide plate 108located above the guide plate 106, and a pair of feed rollers 110 and112 located downstream of (on the left in FIG. 1) the guide plates 106and 108. When a suitable sheet material such as a sheet-like copyingpaper is positioned on the guide plate 106 and advanced to the nippingposition of the feed rollers 110 and 112, these feed rollers 110 and 112nips the sheet material and feeds it. The copying paper fed from thecopying paper feed device 90 between the guide plates 114 and 116 or thesheet material fed from the manual feed device 92 between the guideplates 114 and 118 is passed between guide plates 124 and 126 by theaction of a pair of conveying rollers 120 and 122 and conveyed to aposition between the rotating drum 64 and the transferring coronadischarge device 74 and the peeling corona discharge device 76. Then, bythe action of a suitable conveying belt mechanism 128, it is sent to afixing device 130. Thereafter, it is discharged into a receiving tray134 through an opening 132 formed in the left side surface of thehousing 2 (more specifically, the left side lower surface wall portion18 of the bottom plate 12). The fixing device 130 includes a fixing rollpair comprised of an upper roller 136 and a lower roller 138 cooperatingwith each other (the structure of the fixing device 130 will bedescribed in detail hereinafter). The sheet material from the fixingroller is discharged into the receiving tray 134 by the action of a pairof discharge rollers 140 and 142.

Thus, it will be easily understood with reference to FIG. 1 that theguide plate 108, the feed roller 110, the guide plate 118, the conveyingroller 120 and the guide plate 124 in the sheet material conveyingdevice 88 are mounted on the upper supporting member 6 together with therotating drum 64, the charging corona discharge device 68, the opticalunit 70, the developing device 72, the cleaning means 80, the chargeeliminating lamp 82 and the document illuminating lamp 84. On the otherhand, the copying paper feed device 90, the guide plate 106, the feedroller 112, the guide plate 114, the guide plate 116, the conveyingroller 122, the guide plate 126, the transferring corona dischargedevice 74, the peeling corona discharge device 76, the conveying beltmechanism 128, the fixing device 130 and the receiving tray 134 aremounted on the lower supporting frame 4. Accordingly, when the uppersupporting frame 6 is moved from the closed position shown by the solidline to the open position shown by the two-dot chain line, most of theconveying passage for the sheet material is opened, and therefore in theevent of jamming, the sheet material can be easily taken out from it.

In the copying apparatus described above, the charging corona dischargedevice 68 charges the photosensitive member to a specified polaritysubstantially uniformly while the rotating drum is rotated in thedirection of arrow 66. Then, the image of the document is projected ontothe photosensitive member through the optical unit 70 (at this time, thedocument placing means 48 makes a scanning exposure movement to theright in FIG. 1 from the start-of-scan position shown by the two-dotchain line 48A in FIG. 1) to form on the photosensitive member a latentelectrostatic image corresponding to the document. Thereafter, thedeveloping device 72 applies toner particles to the latent electrostaticimage on the photosensitive member to develop it to a toner image.Subsequently, a sheet material such as copying paper fed from thecopying paper feed device 90 or the manual sheet feed device 92 isbrought into contact with the photosensitive member, and by the actionof the transferring corona discharge device 74, the toner image on thephotosensitve member is transferred to the sheet material. The sheetmaterial is then peeled off from the photosensitive member by the actionof the peeling corona discharge device 76. The sheet material having thetoner image transferred thereto is then conveyed to the fixing device130 where the toner image is fixed. The sheet material having the fixedtoner image is then discharged into the receiving tray 134. In themeantime, the rotating drum 64 continues to rotate. The residual tonerparticles are removed from the photosensitive member by the action ofthe cleaning device 80, and the residual charge on the photosensitivemember is erased by the action of the charge eliminating lamp 82.

Driving System

With reference to FIG. 3 in conjunction with FIG. 1, the driving systemin the illustrated copying apparatus will be described in summary.

In the illustrated copying apparatus, a driving source 144 which may bean electric motor is provided in the upper supporting frame 6. Inrelation to the driving source 144, a power transmission mechanism 146for the rotating drum and an interlocking power transmission mechanism148 are provided in the upper supporting frame 6. The power transmissionmechanism 146 for the rotating drum includes a toothed pulley 150 fixedto the output shaft of the driving source 144, a toothed pulley 152linked to the rotating drum 64, a rotatably mounted tensioning toothedpulley 154, and a timing belt 156 wrapped about these toothed pulleys150, 152 and 154. The interlocking power transmission mechanism 148includes a sprocket wheel 158 fixed to the output shaft of the drivingsource 144, a rotatably mounted sprocket wheel 160, a sprocket wheel 162mounted coaxially, and rotatably as a unit, with the sprocket wheel 160,and a chain 164 wrapped about the sprocket wheels 158 and 160.

The upper supporting frame 6 further has provided therein a powertransmission mechanism 166 for the document placing means and a powertransmission mechanism 168 for the developing device. The powertransmission mechanism 166 for the document placing means includes agear 170 mounted coaxially with, and rotatably as a unit with, thetoothed pulley 152 in the power transmission mechanism 146 for therotating drum, a double clutch means 176 comprising a clutch means 172for normal motion and a clutch means 174 for reverse motion, a gear 178,a pinion gear 180, and a rack 182 (FIGS. 2 and 4) fixed to the lowersurface of the supporting base plate 50 of the document placing means48. With reference to FIGS. 3 and 4 in conjunction with FIG. 1, theclutch means 172 for normal motion has an input gear 183 in mesh withthe gear 170, and the clutch means 174 for reverse motion has an outputgear 185 in mesh with the gear 178. The double clutch means 176comprised of the clutch means 172 and 174 may be substantially the sameas the double electromagnetically controlled spring clutch mechanismdisclosed in the specification and drawings of co-pending JapanesePatent Application No. 47120/1983 entitled "ElectromagneticallyControlled Spring Clutch Mechanism" filed Mar. 23, 1983. Accordingly,the specification and drawings of the above application are cited asreference instead of giving a detailed description of the structure ofthe double clutch means 176.

The gear 178 is engaged with the pinion gear 180, and the pinion gear180 is engaged with the rack 182 extending in the reciprocatingdirection (the left-right direction in FIGS. 1, 3 and 4) of the documentplacing means 48. When the driving source 144 is energized and the gear170 is rotating in the direction of arrow 66, actuation of the clutchmeans 172 for normal motion causes the gear 178 and the pinion gear 180to rotate in the direction shown by an arrow 184, and consequently thedocument placing means 48 is moved at a predetermined speed V in thedirection of arrow 184. On the other hand, when the clutch means 174 forreverse motion is actuated at this time, the gear 178 and the piniongear 180 are rotated in the direction of an arrow 186, and consequently,the document placing means 48 is moved at a speed double the speed V,i.e. 2 V, in the direction of arrow 186.

The power transmission mechanism 168 for the developing device 168includes a gear 188 rotated coaxially with, and rotatably as a unitwith, the sprocket wheels 160 and 162 in the interlocking powertransmission mechanism 148, a gear 190 engaged with the gear 188 and agear 192 engaged with the gear 190. The gear 190 is connected to asleeve member (to be described hereinafter) provided in the developingdevice 72.

A power transmission mechanism 194 which has to do with the conveying ofa sheet material is mounted on the lower supporting frame 4. The powertransmission mechanism 194 includes sprocket wheels 196, 198, 200 and202 and a chain 204 wrapped about these sprocket wheels 196, 198, 200and 202. The sprocket wheel 196 is connected to the feed roller 112(FIG. 1). The sprocket wheel 196 also has provided therein a gear 206coaxially, and rotatably as a unit, with the sprocket wheel 196. A gear208 is engaged with the gear 206, and the gear 208 is connected to thefeed roller 94 (FIG. 1) in the paper feed device 90 through a suitableclutch means (not shown) electromagnetically controlled. The sprocketwheel 198 is connected to the conveying roller 122 through a suitableelectromagnetically controlled clutch means (not shown). The sprocketwheel 200 is provided so as to keep the chain 204 taut. The sprocketwheel 202 is connected to a driven roller 416 (FIG. 1) in the conveyingbelt mechanism 128. The sprocket wheel 202 has attached thereto a gear210 coaxial, and rotatably as a unit, with it. A gear 212 is in meshwith the gear 210, and a gear 214 is in mesh with the gear 212. A gear216 and a gear 218 are kept in mesh with the gear 214, and a gear 220,with the gear 218. The gear 216 is linked to the upper roller 136(FIG. 1) of the fixing device 130, and the gear 220, to a dischargeroller 142.

It will be readily understood from FIGS. 1 and 3 that when the uppersupporting frame 6 is held at the closed position, the sprocket wheel162 of the interlocking power transmission mechanism 148 provided in theupper supporting frame 6 is engaged with the chain 204 of the powertransmission mechanism 194 provided in the lower supporting frame 4 andconsequently, the driving source 144 is drivingly connected to the powertransmission mechanism 194 through the interlocking power transmissionmechanism 148. On the other hand, when the upper supporting frame 6 ismoved to the open position shown by the two-dot chain line in FIG. 1,the sprocket wheel 162 of the interlocking power transmission mechanism148 is brought out of engagement with the chain 204 of the powertransmission mechanism 194.

Automatic Locking Means

As stated hereinabove, the illustrated copying apparatus includes thelower supporting frame 4 and the upper supporting frame 6 mountedthereon for free pivotal movement between the open position and theclosed position, and the document placing means 48 is reciprocallymounted on the upper supporting frame 6. When the upper supporting frame6 is held at the closed position shown by the solid line in FIG. 1, thedocument placing means 48 is positioned substantially horizontally. Butwhen the upper supporting frame 6 is moved from the closed position tothe open position shown by the two-dot chain line in FIG. 1, thedocument placing means 48 is tilted according to the movement of theupper supporting frame 6, and tends to move downwardly to the right inFIG. 1 owing to its own weight, as can be easily seen from FIG. 1. Whenthe upper supporting frame 6 is moved to the open position for disposingof a sheet material jammed in the sheet material conveying passage orotherwise, the driving source 144 is generally deenergizedsimultaneously with, or before the starting of the opening movement ofthe upper supporting frame 6 (for example when the jamming of the sheetmaterial is detected by a suitable means). Accordingly, the drivingsource 144 and the power transmission mechanisms drivingly connecting itto the document placing means 48 (i.e., the power transmission mechanism146 for the rotating drum and the power transmission mechanism 166 forthe document placing means 48) have no sufficient resisting force tohamper the aforesaid movement of the document placing means 48. Hence,unless some means for checking the movement of the docmuent placingmeans 48 is provided, the document placing means 48 moves freelydownwardly to the right in FIG. 1, and may collide with an objectlocated around the copying apparatus, for example, resulting in a damageto itself and/or the object.

Accordingly, in the illustrated copying apparatus improved in accordancewith this invention, a relatively simple and inexpensive automaticlocking means is provided in order to hamper the free movement of thedocument placing means 48 accurately during the opening movement of theupper supporting frame 6.

With reference to FIGS. 2 and 4, two projections 222 located atdiametrically opposite positions are formed in the front surface of thegear 178 of the power transmission mechanism 166 for the documentplacing means in the illustrated embodiment. A locking member 224 isdisposed in relation to the projections 222. The locking member 224formed of a slender rod is mounted on the vertical front base plate 20and the vertical rear base plate 22 of the upper supporting frame 6 forfree movement in the front-rear direction (the left-right direction inFIG. 2). An annular flange 226 located slightly rearwardly (to the leftin FIG. 2) of the vertical front base plate 20 is formed in the lockingmember 224. A spring means 228 composed of a compression coil spring isdisposed between the annular flange 226 and the vertical front baseplate 20. The spring means 228 elastically biases the locking means 224rearwardly (to the left in FIG. 2). The front end portion of the lockingmember 224 projects forwardly beyond the vertical front base plate 20,and a lock cancelling mechanism 230 is provided in relation to thisfront end portion. The lock cancelling mechanism 230 includes a pivotmember 236 pivotally mounted by a pin 234 on a supporting piece 232fixed to the front surface of the vertical front base plate 20. One endportion, i.e. the upper end portion 238, of this pivot member 236 is ofa bifurcated shape striding over the front end portion of the lockingmember 224. To the locking member 224 is fixed a pin 240 which extendsin front of the bifurcated upper end portion 238 of the pivot member 236in a direction perpendicular to the sheet surface in FIG. 2, andcooperates with the bifurcated upper end portion 238 of the pivot member236. On the other hand, the other end portion, i.e., the lower endportion 242, of the pivot member 236 is slightly inclined downwardly andrearwardly (to the left in FIG. 2). In relation to this lower endportion 242 of the pivot member 236, an engaging piece 244 of anL-shaped cross section is secured to the front surface of the verticalfront base plate 8 of the lower supporting frame 4.

The operation of the automatic locking means described above will bedescribed. When the upper supporting member 6 is held at the closedposition shown by the solid line in FIG. 2, the engaging piece 244 actson the lower end portion 242 of the pivot member 236 to hamper thecounterclockwise pivoting of the pivot member 236 in FIG. 2, and thusrestrains the pivot member 236 at an operating position shown by a solidline in FIG. 2. When the pivot member 236 is restrained at the operatingposition, the bifurcated upper end portion 238 of the pivot member 236acts on the pin 240 fixed to the locking member 224, and urges thelocking member 224 to a lock cancelling position shown by a solid linein FIG. 2 against the elastic biasing action of the spring means 228.When the locking member 224 is forcibly held at the lock cancellingposition, the rear end of the locking member 224 is located slightlyforwardly of the front end of the projections 222 formed in the frontsurface of the gear 178, and therefore, the rear end of the lockingmember 224 does not hamper rotation of the gear 178 by interfering withthe projections 222.

On the other hand, when the upper supporting frame 6 is somewhat movedtoward the open position shown by the two-dot chain line in FIG. 2 fromthe closed position shown by the solid line in FIG. 2, the lower endportion 242 of the pivot member 236 comes out of engagement with theengaging piece 244, thus permitting the counterclockwise pivoting of thepivot member 236 in FIG. 2. As a result, the locking member 224 is movedrearwardly (to the left in FIG. 2) by the elastic biasing action of thespring means 228, and held at a locking position at which its rear endabuts against the front surface of the gear 178. Simultaneously, the pin240 fixed to the locking member 224 acts on the bifurcated upper endportion 238 of the pivot member 236, and the pivot member 236 is held ata non-operating position shown by a two-dot chain line in FIG. 2.

As will be readily understood from FIG. 4, the rear end of the lockingmember 224 which has abutted against the front surface of the gear 178is located within the rotating trajectory of the projections 222 formedin the front surface of the gear 178 and interferes with the rotation ofthe projections 222. Hence, at whatever angular position the gear 178exists, either one of the two projections 222 abuts against the rear endof the locking member 224 before the gear 178 rotates through an angleof 180° and the rotation of the gear 178 is thus hampered. Let ussuppose that at the beginning of the opening movement of the uppersupporting frame 6 from the closed position toward the open position,the rear end of the locking member 224 is located in alignment witheither one of the two projections 222. At this time, even when thelocking member 224 is moved rearwardly by the elastic biasing action ofthe spring means 228, the rear end of the locking member 224 abutsagainst the front surface of either one of the two projections 222whereby the locking member 224 is not moved to the aforesaid lockingposition. When at this time the gear 178 is rotated slightly (and thedocument placing means 48 is slightly moved), the alignment of eitherone of the projections 222 with the locking member 224 is cancelled, andtherefore, the locking member 224 is moved to the locking position bythe elastic biasing action of the spring means 228, thereby checking therotation of the gear 178. Since as stated above the gear 178 isconnected via the pinion gear 180 to the rack 182 fixed to the undersurface of the document placing means 48, checking of the rotation ofthe gear 178 causes the document placing means 48 to stop moving. Itwill be evident therefore that when the upper supporting frame 6 startsits opening movement from the closed position toward the open position,the automatic locking means automatically acts irrespective of theposition of the document placing means 48 at this time, therebyhampering the movement of the document placing means 48 and permitingits movement corresponding only to approximately the half rotation ofthe gear 178 at the largest. In the illustrated embodiment, twoprojections 222 are formed in the front surface of the gear 178. But itis possible to form only one projection, or three or morecircumferentially spaced projections. It will be readily understood thatwhen only one projection is formed, the maximum amount of movement ofthe document placing means 48 which can occur after the upper supportingframe 6 started movement from the closed position to the open positionis increased to an amount corresponding to about one rotation of thegear 178, and that when three or more projections are formed, themaximum amount of movement of the document placing means 48 which canoccur after the opening movement of the upper supporting frame 6 fromthe closed position toward the open position is decreased according toan increase in the number of projections.

When the upper supporting frame 6 is moved to near the closed positionin its closing movement from the open position shown by the two-dotchain line in FIG. 2 toward the closed position shown by the solid linein FIG. 2, the tilted lower end portion 242 of the pivot member 236abuts against the upper end of the engaging piece 244. Thereafter, thepivot member 236 undergoes the action of the engaging piece 244according to the closing movement of the upper supporting frame 6 and ispivoted clockwise in FIG. 2. When the upper supporting frame 6 reachesthe closed position, the pivot member 236 is restrained at the operatingposition shown by a solid line in FIG. 2 by the engaging piece 244. Inthis manner, while the pivot member 236 is pivoted from thenon-operating position shown by the two-dot chain line in FIG. 2 to theoperating position shown by the solid line in FIG. 2, the bifurcatedupper end portion of the pivot member 236 acts on the pin 240 fixed tothe locking member 224 to move the locking member 224 from the lockingposition shown by the two-dot chain line in FIG. 2 to the lockcancelling position shown by the solid line in FIG. 2. Consequently,when the upper supporting frame 6 is brought to the closed position,hampering of the rotation of the gear 178 and therefore hampering of themovement of the document placing means 48 are automatically cancelled.

In the above specific embodiment, the projections 222 are formed in thefront surface of the gear 178. If desired, grooves may be formed insteadof the projections 222 so that when the locking member 224 is held atthe locking position, its rear end advances into the grooves.Alternatively, it is possible to form projections or grooves in thepinion gear 180, for example, instead of the gear 178, and provide thelocking member 224 in relation of such projections or grooves. Iffurther desired, it is possible to form a plurality of projections orgrooves at suitable intervals in the reciprocating direction of thedocument placing means 48 on the side surface of the rack 182 fixed tothe under surface of the document placing means 48 or at suitablepositions of the document placing means 48, and to provide the lockingmember 224 in relation to such projections or grooves.

FIG. 5 shows a modified example of the automatic locking means. In thismodified example, the front cover 36' is formed integrally ranging fromits lower end to its upper end. The front cover 36' is mounted on thelower supporting frame 4' for free pivoting movement between a closedposition shown by a solid line and an open position shown by a two-dotchain line by linking its lower end portion to the front edge portion ofthe bottom plate 14' of the lower supporting member 4' through a hingemeans 246. It will be readily understood that in the modified example,the front cover 36' needs to be moved from the closed position to theopen position prior to moving the upper supporting frame 6' from theclosed position to the open position, and the front cover 36' needs tobe moved from the open position to the closed position after the uppersupporting frame 6' has been moved from the open position to the closedposition. In this embodiment, the restraining of the lock cancellingmechanism 230 may be cancelled by moving the front cover 36' from theclosed position toward the open position instead of cancelling it bymoving the upper supporting frame 6' from the open position toward theclosed position.

In the modified example illustrated in FIG. 5, an engaging piece 244'extending rearwardly (to the left in FIG. 5) is fixed to the rearsurface of the front cover 36'. When the front cover 36' is held at theclosed position, the engaging piece 244' acts on the lower end portion242' of the pivot member 236' to restrain the pivot member 236' at theoperating position shown by a solid line, and thus, the locking member224' is maintained at the lock cancelling position against the elasticbiasing action of the spring means 228'. When the front cover 36' startsto move from the closed position toward the open position, the engagingpiece 244' comes out of engagement with the lower end portion 242' ofthe pivot member 236', and therefore, the restraining of the pivotmember 236' is cancelled. As a result, the locking member 224' is movedto the locking position by the elastic biasing action of the springmeans 228', and at the same time, the pivot member 236' is pivoted tothe non-operating position shown by the two-dot chain line.

Otherwise, the structure of the modified embodiment shown in FIG. 5 issubstantially the same as the embodiment described hereinabove.

In the modified embodiment shown in FIG. 5, the lock cancellingmechanism 230' is operated according to the opening and closing movementof the front cover 36'. When the copying apparatus includes anothermember which is moved to an open position prior to the opening movementof the upper supporting frame 6' and to a closed position after closingmovement of the upper supporting frame 6', the lock cancelling mechanism230' can be adapted to be operated according to the opening and closingmovement of the other member.

When the power transmission mechanism 166 for the document placing meansinterposed between the document placing means 48 and the driving source144 includes the clutch means 172 for normal motion and the clutch means174 for reverse motion as in the illustrated copying apparatus, themovement of the document placing means 48 may also be hampered bydetecting the starting of the opening movement of the upper supportingframe 6 from the closed position toward the open position (or thestarting of the opening movement of the front cover 36' from the closedposition toward the open position), and simultaneously operating theclutch means 172 and 174.

With reference to FIG. 6, a detecting means 248 which may be constructedof a limit switch, a reed switch, or the like is off when the uppersupporting frame 6 (or the front cover 36') is at the closed position,but when the upper supporting frame 6 (or the front cover 36') is movedslightly from the closed position toward the open position, it is turnedon to generate a signal. The signal is fed to a control means 250 whichmay be a microprocessor provided in a copying apparatus for variouscontrolling purposes. Upon receipt of the above signal, the controlmeans 250 simultaneously actuates the clutch means 172 for normal motionand the clutch means 174 for reverse motion. As a result, by the mutualaction of the clutch means 172 and 174, the movement of the powertransmission mechanism 166 for the document placing means is hamperedaccurately, and therefore, the movement of the document placing means 48is hampered accurately.

In order for the automatic locking means to act effectively, the powersupply switch for coupling a commercial power supply, etc. to thecopying apparatus needs to be closed. Or a battery at least for thedetecting means 248, the control means 250, the clutch means 172 fornormal motion and the clutch means 174 for reverse motion should bebuilt in the copying apparatus. In addition, it is important that thecontrol means 250 should deenergize the driving source 144simultaneously with, or before, the simultaneous actuation of theclutches 172 and 174. Otherwise, the driving force transmitted from thedriving source 144 would damage the clutch means 172 and 174, or thedriving source 144 would be injured. In view of this, it is preferredthat when the detecting means 248 is closed to produce the aforesaidsignal, the control means 250 should deenergize the driving source 144if the driving source 144 has been energized up to that time, and thatsimultaneously with it, or after some delay of time, it shouldsimultaneously actuate both the clutch means 172 and 174.

Some specific embodiments of the automatic locking means have beendescribed hereinabove with reference to the hampering of the movement ofthe document placing means. The automatic locking means described abovecan also be applied to the automatic hampering of a part or the whole ofthe optical system in a copying apparatus of the type in which a part orthe whole of the optical unit is mounted reciprocably on the uppersupporting frame (and therefore, in scanning and exposing a document,not the document placing means but the whole or part of the optical unitis moved ) instead of mounting the document placing means reciprocablyon the upper supporting frame.

Latent Electrostatic Image Developing Device

Now, a detailed description will be made of the structure of thedeveloping device 72 for applying toner particles to a latentelectrostatic image formed on the photosensitive member on theperipheral surface of the rotating drum 64 to develop it to a tonerimage.

With reference to FIG. 7, the illustrated developing device 72 includesa development housing 258 defined by a front and a rear wall 252 (onlythe rear wall is shown in FIG. 7) spaced from each other in thefront-rear direction (a direction perpendicular to the sheet surface inFIG. 7), a recessed bottom wall 254 and a side wall 256. The lowerportion of the development housing 258 defines a developer receptacle259 for accommodating a two-component developer 260 composed of carrierparticles and toner particles.

A developer applicator means 262 is disposed within the developmenthousing 258. The developer applicator means 262 in the illustratedembodiment is comprised of a cylindrical sleeve member 266 adapted to berotated in the direction of an arrow 264 and a stationary permanentmagnet 268 disposed within the sleeve member 266. The stationarypermanent magnet 268 is in roll form, and has a plurality of magneticpoles circumferentially spaced from each other at its peripheral edgeportion (three S poles and two N poles therebetween).

Around the sleeve member 266 of the developer applicator means 262, adeveloper drawing zone 270, a brush length-adjusting zone 272, adeveloping zone 274 and a developer removing zone 276 are located inthis order as viewed from the rotating direction of the sleeve member266 shown by an arrow 264. The developer drawing zone 270 is disposed inone side portion (the right side portion in FIG. 7) of the sleeve member266, and the brush length-adjusting zone 272 is provided inapproximately the topmost portion of the sleeve member 266. Thedeveloping zone 274 is disposed in the other side portion (the left sideportion in FIG. 7) of the sleeve member 266. Conveniently, the developerremoving zone 276 is provided in the one side portion of the sleevemember 266 and below the developer drawing zone 270.

A brush length-adjusting member 278 is provided in the brushlength-adjusting zone 272. In the illustrated embodiment, a suspendedpiece extending downwardly from the under surface of a member 280secured to the inner surface of the side wall 256 forms the brushlength-adjusting member 278. The tip of the brush length-adjustingmember is in approximity to the sleeve member 266 in its circumferentialdirection with some clearance which may, for example, be about 1 mm. Inthe developing zone 274, the peripheral surface of the sleeve member 266faces the peripheral surface of the rotating drum 64 with some clearnacethrough an opening 282 defined between the lower end edge of the sidewall 256 and one edge of the bottom wall 254.

Within the development housing 258, there is disposed a developeragitating means comprised of a rotary agitating mechanism 286 adapted tobe rotated in the same direction as the rotating direction of the sleevemember 266 shown by the arrow 264. As is clear from FIG. 7, the rotaryagitating mechanism 286 is positioned so as to adjoin the sleeve member266 in a region ranging from the developer removing zone 276 to thedeveloper drawing zone 270. With reference to FIG. 8 taken inconjunction with FIG. 7, the illustrated rotary agitating mechanism 286has a rotating shaft portion 288 extending substantially parallel to theaxis of rotation of the sleeve member 266, circular end plate portions290 fixed respectively to the opposite end portions of the rotatingshaft portion 288, and a plurality of (12 in the illustrated embodiment)agitating blade portions 292 extending between the two end plateportions 290 at circumferentially spaced positions. Each of theagitating blade portions 292 in the radial direction extends from itsinside end connected to the rotating shaft portion 288 to its outsideend in a concabe shape. In the front-rear direction (a directionperpendicular to the sheet surface in FIG. 7), it extends from its frontend side to its rear end side while it is inclined on the upstream sideas viewed in the rotating direction shown by an arrow 284.

A partitioning plate 294 is also provided in the development housing258. The ijlustrated partitioning plate 294 has an inclined portion 296extending upwardly from its lower end located above the rotary agitatingmechanism 286 while it is inclined to the left in FIG. 7, and ahorizontal upper end portion 298 extending from this inclined portion296 substantially horizontally to the left in FIG. 7. The horizontalupper end portion 298 is located somewhat upstream of the brushlength-adjusting zone 272 in which the brush length-adjusting member 278is located. As clearly shown in FIG. 8, a plurality of (8 in thedrawing) guide protrusions 300 spaced from each other in the widthwisedirection of the upper surface of the inclined portion 296 (i.e., thefront-rear direction perpendicular to the sheet surface in FIG. 7) areprovided on the upper surface of the inclined portion 296. Each of theguide protrusions 300 is inclined from its rear end toward its front endin the direction of its lower end, i.e. toward the rotary agitatingmechanism 286. A relatively narrow projecting piece 302 extendingdownwardly from its nearly intermediate portion in its widthwisedirection is provided in the upper edge of the horizontal upper endportion 298 of the partitioning plate 294. The lower end of theprojecting piece 302 approximates the peripheral surface of the sleevemember 266 preferably at an angular position at which one of themagnetic poles of the stationary permanent magnet 268 is located, or itsvicinity. The distance between the lower end of the projecting piece 302and the peripheral surface of the sleeve member 266 is smaller than thatbetween the lower end of the brush length-adjusting member 278 and theperipheral surface of the sleeve member 266, and is desirably about 0.5mm, for example.

To the top of the member 280 is fixed a contact-type developer detector304 of a known type which detects the inductance of the developer 260corresponding to the ratio between the carrier particles and the tonerparticles. It will be readily understood with reference to FIGS. 7 and 9that a circular opening 306 is formed in the member 280, and a circulardetecting portion 308 of the developer detector 304 is located in theopening 306. The lower end surface of the circular detecting portion 308constitutes a developer contacting surface 310, and the developerdetector 304 detects the inductance of the developer 260 contacting thedeveloper contacting surface 310. As illustrated in FIG. 9, thedeveloper contacting surface 310 is positioned preferably adjacent tothe one side of the projecting piece 302 mentioned above as viewed inthe widthwise direction (i.e., the front-rear direction).

A toner particle receptacle 314 for accommodating toner particles isdisposed in the upper portion of the development housing 258, and atoner particle discharge opening 316 is formed in the lowermost portionof the toner particle receptacle 314. Preferably, the toner particledischarge opening 316 is located above the rotary agitating mechanism286 and adjacent to the lower end of the paritioning plate 294. A tonerparticle feed means 318 is annexed to the toner particle dischargeopening 316. In the illustrated embodiment, the toner particle feedmeans 318 is comprised of a toner particle feed roller 320 rotatablymounted just above the toner particle discharge opening 316. Manydepressed portions or grooves are formed on the peripheral surface ofthe toner particle feed roller 320. The toner particle feed roller 320is selectively rotated in the direction shown by an arrow 370 accordingto the inductance of the developer detected by the developer detector304. As a result, toner particles 3212 are received in many depressedportions or grooves present on the peripheral surface of the tonerparticle feed roller 320 and carried to the toner particle dischargeopening 316, and then through the toner particle discharge opening 316,are caused to flow onto the rotary agitating mechanism 286. Thus, thetoner particles 312 are fed into the developer receptacle 259 from thetoner particle receptacle 314. Means for selectively rotating the tonerparticle feed roller 320 according to the inductance of the developerdetected by the developer detector 304 will be described hereinafter.

In the developing device 72 described above, the rotation of the sleevemember 266 of the developer applicator means 262 in the direction ofarrow 264 brings about the following actions. With reference to FIG. 7,in the developer drawing zone 270, a part of the developer 260 presentin the developer receptacle 259 is attracted to, and held on, theperipheral surface of the sleeve member 266 by the magnetic attractingforce of the stationary permanent magnet 268. The developer 260 held onthe peripheral surface of the sleeve member 266 is gradually raised bythe rotation of the sleeve member 266 and carried to the brushlength-adjusting zone 272. As will be readily understood from FIG. 7,the developer 260 moves below the partitioning plate 294 at this time.Slightly upstream of the brush length-adjusting zone 272 is located therelatively narrow projecting piece 302 approximating the peripheralsurface of the sleeve member 266. By the action of the projecting piece302 upon the developer 260 held on the peripheral surface of the sleevemember 266, a considerable amount of the developer 260 is removed fromthe peripheral surface of the sleeve member 266 at its central portionin the front-rear direction (the direction perpendicular to the sheetsurface in FIG. 7) at which the projecting piece 302 exists. As shown byan arrow 322 in FIG. 9, however, the developer 260 flows inwardly in thefront-rear direction from both sides of the projecting piece 302downstream of the projecting piece 302, and therefore even at thecentral portion in the front-rear direction, a considerable amount ofthe developer 260 is held on the peripheral surface of the sleeve member266. The advantage obtained by the flowing of the developer 260 in thedirection of arrow 322 which is caused by the projecting piece 302 willbe described hereinafter.

In the brush length-adjusting zone, the brush length-adjusting member278 acts on the developer 260 held on the peripheral surface of thesleeve member 266 to remove the excess of the developer 260 therefromand adjusts the thickness of the layer of the developer 260 held on theperipheral surface of the sleeve member 266, i.e. the brush length, to arequired value. The developer 260 removed from the peripheral surface ofthe sleeve member by the action of the brush length-adjusting member 278is conducted to the surface of the horizontal upper end portion 298 ofthe partitioning plate 294 and then flows over the inclined portion 296and onto the rotary agitating mechanism 286. The developer 260 which hasbeen removed from the peripheral surface of the sleeve member 266 andintroduced into the horizontal upper end portion 298 contacts thedeveloper contacting surface 310 of the developer detector 304, andtherefore, the developper detector 304 detects the inductance of thedeveloper 260.

The developer 260 held on the peripheral surface of the sleeve member266 is then carried to the developing zone 274 by the rotation of thesleeve member 266 and brought into contact with the photosensitivemember on the rotating drum 64 rotating in the direction of arrow 66.Consequently, the toner particles in the developer 260 are applied to alatent electrostatic image on the photosensitive member and the image isdeveloped into a toner image.

Subsequently, the developer 260 held on the peripheral surface of thesleeve member 266 is carried to the developer removing zone 276 by therotation of the sleeve member 266. In the developer removing zone 276,no magnetic pole exists in the stationary permanent magnet, andtherefore its magnetic attracting force is extremely small. Moreover,the flow of the developer 260 agitated by the rotary agitating mechanism286 rotating in the direction of arrow 284 acts on the peripheralsurface of the sleeve member 266. Accordingly, the developer 260 isremoved from the peripheral surface of the sleeve member 266 in thedeveloper removing zone 276.

The rotary agitating mechanism 286 rotating in the direction of arrow284 agitates the developer 260 removed from the sleeve member 266 in thedeveloper removing zone 276, the developer 260 flowing onto the rotaryagitating mechanism 286 after flowing over the partitioning plate 294,and the toner particles 312 which flow onto the rotary agitatingmechanism 286 from the toner particle discharge opening 316 of the tonerparticle receptacle 314 by the action of the selectively rotated tonerparticle feed roller 320, and thus uniformly mixes the carrier particlesand the toner particles in the developer 260 and triboelectricallycharges the toner particles to a specified polarity. Thereafter, itfeeds the developer to the developer drawing zone 270.

As clearly shown in FIGS. 8 and 9, the plurality of guide protrusions300 spaced from each other in the widthwise direction are provided onthe upper surface of the inclined portion 296 of the partitioning plate294. Each of the guide protrusions 300 is inclined from its rear end toits front end toward the rotary agitating mechanism 286. Hence, thedeveloper 260 which flows over the partitioning plate 294 and onto therotary agitating mechanism 286 is moved from its rear end to its frontend. On the other hand, each of the plurality of the agitating bladeportions 292 provided in the rotatary agitating mechanism 286 extendsinclinedly from its front end toward its rear end in the upstreamdirection as viewed in the rotating direction shown by the arrow 284.Accordingly, the developer 260 carried in the direction of arrow 284 bythe rotary agitating mechanism 286 is moved from the front end to therear end of each agitating blade. Thus, in the illustrated developingdevice 72, the developer 260 is mixed also in the widthwise direction(i.e., the front-rear direction perpendicular to the sheet surface inFIG. 7) and fully made uniform in the widthwise direction as well. Ithas already been known to mix a developer in the widthwise direction bythe action of a combination of a plate-like member having a plurality ofinclined guide protrusions on its upper surface and a rotary agitatingmechanism. However, in the known technique, the agitating blade portionsformed in the rotary agitating mechanism are spaced from each other inthe widthwise direction and are helical in shape. Hence, the effect ofmovement of the developer from one end to the other by the rotaryagitating mechanism is not entirely sufficient, and therefore, themixing of the developer in the widthwise direction is not sufficient. Incontrast, in the developing device 72 described above which has beenimproved in accordance with the present invention, each of the pluralityof agitating blade portions 292 provided in the rotary agitatingmechanism 286 extends continuously in an inclined manner from one end tothe other. For this reason, the developer 260 is moved sufficientlyeffectively from one end to the other by the action of the rotaryagitating mechanism 286, and therefore fully mixed and made uniform inthe widthwise direction.

In the illustrated developing device 72, the developer 260 is mixed inthe widthwise direction by the combined action of the partitioning plate294 having the inclined guide protrusions 300 and the rotary agitatingmechanism 286 having the special agitating blade portions 292. Ifdesired, instead of this arrangement, it is possible to provide tworotary agitating mechanism having special agitating blade portions sideby side and mix the developer in the widthwise direction by the combinedaction of the two rotary agitating mechanisms. It is of course importantin this case that the agitating blade portions in one rotary agitatingmechanism should be inclined upstream in the rotating direction from oneend to the other and the agitating blade portions in the other rotationrotary agitating mechanism should be inclined downstream in the rotatingdirection from one end to the other, in order for one rotary agitatingmechanism to move the developer from one end to the other and the otherrotary agitating mechanism to move it from the other end to one end.

In the aforesaid developing device 72, the following points should alsobe noted. Specifically, the developer detector 304 should detect thedeveloper 260 which has been sufficiently agitated and mixed. Otherwise,it is impossible to detect a value corresponding to the actual ratiobetween carrier particles and toner particles in the developer 260.Furthermore, the developer 260 detected by the developer detector 304should be the one immediately after mixing and should not be the onewhich has a tendency to reside at a specified locality of the developerreceptable. When the developer 260 detected has a tendency to reside ata specified locality of the developer receptacle 259, it will be readilyseen that the detector cannot detect the actual ratio which varies withthe performance of development. Furthermore, as a matter of course, thecontacting of the developer 260 with the developer contacting surface310 of the developer detector 304 should not adversely affect thedeveloping action. In the developing device 72 described above which hasbeen improved by the present invention, the developer 260 which has beenfully agitated and mixed by the rotary agitating mechanism 286, fed tothe developer drawing zone 270, carried to the brush length-adjustingzone 272 while being held onto the peripheral surface of the sleevemember 266, removed from the peripheral surface of the sleeve member 266by the action of the brush length-adjusting member 278 in the brushlength-adjusting zone 272, and introduced onto the partitioning plate294 is brought into contact with the developer-contacting surface 310 ofthe developer detector 304. Accordingly, the developer 260 which hasjust been agitated and mixed sufficiently and having substantially thesame carrier-toner ratio as the developer 260 carried to the developingzone 274 from the brush length-adjusting zone 272 makes contact with thedeveloper contacting surface of the developer detector 304. Furthermore,the developer 260 to be contacted with the developer-contacting surface310 of the developer detector 304 while being held on the peripheralsurface of the sleeve member 266 is gradually raised from the developerdrawing zone 270 to the upstream side of the brush length-adjusting zone272 against the action of gravity. Then, by the action of the brushlength-adjusting member 278, its moving direction is forcibly reversed,and then it is introduced onto the partitioning plate 294. Accordingly,the developer 260 contacting the developer-contacting surface 310 iscaused to flow very well without stagnation. Furthermore, in theillustrated embodiment, the projecting piece 302 is provided slightlyupstream of the brush length-adjusting zone 272, and owing to thepresence of the projecting piece 302, the flow of the developer 260 inthe direction of arrow 322 in FIG. 9 is forcibly formed, as satedhereinabove. As shown in FIG. 9, the developer contacting surface 310 ofthe detector 304 is positioned adjacent to one side of the projectingpiece 302. Hence, the developer 260 present near thedeveloper-contacting surface 310 flows more accurately under theinfluence of the flow of the developer 260 shown by arrow 322 in FIG. 9.Furthermore, since the developer 260 contacting the developer-contactingsurface 310 has been removed from the peripheral surface of the sleevemember 266 by the action of the brush length-adjusting member 278 in thebrush length-adjusting zone 272, there is no likelihood that developmentin the developing zone 274 will be adversely affected by the contactingof the developer 260 with the developer contacting surface 310 of thedeveloper detector 304. For the foregoing reason, the inductance of thedeveloper 260 can be properly detected by the developer detector 304without adversely affecting the developing zone 274 in the developingdevice 72 in accordance with this invention.

The toner particle feed roller control means in the developing device 72will be described in detail.

This control means controls the rotation of the toner particle feedroller 320 according to the inductance of the developer 260 detected bythe developer detector 304, and therefore controls the supplying oftoner particles from the toner particle receptacle 314 to the developerreceptacle 259 according to variations in the ratio of the carrierparticles and the toner particles in the developer, thereby maintainingthe ratio of the carrier particles and the toner particles in thedeveloper 260 at a specified value within a required range. Withreference to FIGS. 7 and 10, the rotating shaft 324 to which the sleevemember 266 is fixed projects rearwardly beyond the rear wall 252 of thedevelopment housing 258, and the gear 192 already referred to withreference to FIG. 3 (i.e., the gear 192 in the power transmissionmechanism 168 for the developing device) is fixed to the projecting endportion of the rotating shaft 324. The rotating shaft 326 having therotary agitating mechanism 286 fixed thereto also projects rearwardlybeyond the rear wall 252 of the development housing 258, and a gear 328is fixed to the projecting end portion of the rotating shaft 326. Ashort shaft 330 is fixed to the rear wall 252 of the development housing258, and a gear 332 is rotatably mounted on the short shaft 330. Thegear 332 is in mesh with both the gear 192 and the gear 328.Accordingly, when the gear 192 and the sleeve member 266 are rotated inthe direction of arrow 264 by the driving force transmitted from thedriving source 144 (FIG. 3), the gear 332 is rotated in the directionshown by an arrow 334, and the gear 328 and the rotary agitatingmechanism 286 are rotated in the direction of arrow 284.

A cam 336 constituting part of the toner particle feed roller controlmeans is also mounted on the short shaft 330 so that it can rotate as aunit with the gear 332. Conveniently, the cam 336 is an eccentric camformed of a disc mounted eccentrically on the short shaft 330. Therotating shaft 338 to which the toner particle feed roller 320 is fixedalso projects rearwardly beyond the rear wall of the toner particlereceptacle 314. With reference to FIGS. 10 and 11, a one-way clutch 340known per se is mounted on the projecting end portion of the rotatingshaft 338, and a lever member 342 is mounted to the one-way clutch 340.The lever member 342 includes a hub portion 344 to be received about theone-way clutch 340, a cam follower portion 346 extending radiallyoutwardly from the hub portion 344 and a restrained portion 348. Therestrained portion 348 is nearly hool-shaped, and its peripheral edgedefines an arcuate edge 350 with the central axis of the rotating shaft338 as a center. A notch 352 is formed in the arcuate edge 350. A springmember 354 which may be a helical spring is received about the hubportion 344 of the lever member 342. One end 356 of the spring means 354is engaged with one edge of the restrained portion 348 of the levermember 342, and its other end 358, with a suitable engaging projection(not shown) provided in the rear surface of the rear wall 252 of thedevelopment housing 258. Thus, the spring means 354 elastically biasesthe lever member 342 counterclockwise in FIG. 10 to cause one side edgeof the cam follower portion 346 of the lever member 342 to abut againstthe peripheral edge of the cam 336. A securing bracket 360 is also fixedto the rear surface of the rear wall of the toner particle receptacle314. An electromagnetic means 362 which may be a solenoid is secured tothe securing bracket 360. Furthermore, a restraining member 364 ismounted on the securing bracket 360 so that it can freely pivot betweenan operating position shown by a solid line in FIG. 10 and anon-operating position shown by a two-dot chain line in FIG. 10. One endof the restraining member 364 has formed therein a projection 366 whichcooperates with the notch 352 formed in the arcuate edge 350 of therestrained portion 348 of the lever member 342 when the restrainingmember 364 is at the operating position. A spring means 368 which may bea tension coil spring is stretched across the other end portion of therestraining member 364 and the securing bracket 360. The spring means368 elastically biases the restraining member 364 to the operatingposition.

In the toner particle supply roller control means described above, theelectromagnetic means 362 is adapted to be energized and deenergizedaccording to the characteristic value of the developer 260 detected bythe developer detector 304, and therefore to the ratio of the carrierparticles and the toner particles in the developer 260. When theelectromagnetic means 362 is energized, the restraining member 364 ispivoted to the non-operating position shown by the two-dot chain line inFIG. 10 against the elastic biasing action of the spring means 368. As aresult, the projection 366 of the restraining member 364 comes out ofengagement with the notch 352 formed in the restrained portion 348 ofthe lever member 342 and the restraining of the lever member 342 by therestraining member 364 is cancelled. Consequently, the lever member 342is reciprocated between one limit angular position shown by a solid linein FIG. 10 and another limit angular position shown by a two-dot chainline in FIG. 10 by the cooperation of the cam 336 rotated in thedirection of an arrow 334 with the spring means 354 for elasticallycontacting the cam follower portion 346 of the lever member 342 with theperipheral edge of the cam 336. When the lever member 342 is pivotedfrom the other limited angular position to the one limit angularposition clockwise in FIG. 10, the pivotal movement of the lever member342 is transmitted to the rotating shaft 338 through the one-way clutch340, and the toner particle supply roller 320 is rotated in thedirection of an arrow 370 (FIG. 7). On the other hand, when the levermember 342 is pivoted counterclockwise in FIG. 10 from the one limitangular position to the other limit angular position, the one-way clutch340 does not transmit its pivotal movement to the rotating shaft 338,and therefore, the toner particle supply roller 320 is not rotated.Thus, when the lever member 342 is reciprocally pivoted between the onelimit angular position to the other limit angular position, the tonerparticle supply roller 320 is intermittently rotated in the direction ofarrow 370.

When the electromagnetic means 362 is deenergized, the spring means 368elastically biases the restraining member 364 toward the operatingposition shown by the solid line in FIG. 10, and pushes the projection366 of the restraining member 364 against the arcuate edge 350 of therestrained portion 348 of the lever member 342. When in this state thelever member 342 is held at the one limit angular position shown by thesolid line in FIG. 10 at which the largest diameter portion of the cam336 acts on the cam follower portion 346 of the lever member 342, therestraining member 364 is held at the position shown by a solid line inFIG. 10, and the projection 366 of the restraining member 364 is engagedwith the notch 352 formed in the arcuate edge 350 of the restrainedportion 348 of the lever member 342. As a result, the lever member 342is restrained at the aforesaid one limit angular position, and in spiteof the rotation of the cam 336, the lever member 342 is not pivoted andtherefore the toner particle feed roller 320 is not rotated.

It may be possible in the aforesaid toner particle feed rollercontrolling means to omit the restraining member 364 and the springmeans 368 and cause the electromagnetic means 362 to act directly on thelever member 342 so that when the electromagnetic means 360 is energizedthe lever member 342 is restrained at the one limit angular positionshown by the solid line in FIG. 10. However, this requires a relativelystrong and expensive electromagnetic means which restrains the levermember 342 at the one limit angular position directly in resistance tothe relatively strong spring means 354 that elastically biases the levermember 342 counterclockwise in FIG. 10 and contacts the cam followerportion 346 of the lever member 342 with the peripheral edge of the cam336. As a result, the toner particle feed roller control means willbecome relatively expensive. In contrast, in the toner particle feedroller controlling means described above, the electromagnetic means 362needs only to be able to hold the restraining member 364 at thenon-operating position shown by the two-dot chain line in FIG. 10against the elastic biasing force of the spring means 368 which may berelatively weak. Accordingly, the toner particle feed roller controllingmeans may be one which is relatively weak and inexpensive.

Fixing Device

In the fixing device used in the electrostatic copying apparatusdescribed above, a toner image on a sheet meterial is fixed on itssurface by conveying the sheet material having the toner imagetransferred in the transferring zone between a pair of fixing rollers.Generally, in such a fixing device, the downstream end of a guide memberprovided upstream of the pair of fixing rollers for guiding the sheetmaterial to the fixing rollers (i.e., that end of the guide member whichis in proximity to the pair of fixing rollers) is positioned above thenip position of the pair of fixing rollers. When the downstream end ofthe guide member is so positioned, a sheet material of relatively lowstiffness which is frequently used is bent by the downstream end of theguide member, and by this bending action, creases of that portion of thesheet material which is introduced between the fixing rollers arestraightend, and it is possible to prevent the occurrence of creases onthe sheet material during fixing by the fixing rollers. On the otherhand, when a sheet material having relatively high stiffness [forexample, an official postal card (which is not often used)] is used, theleading end of the sheet material contacts the upper fixing roller inthe fixing roller pair and conveying of the sheet material may fail(jamming occurs). Or the trailing end portion of the sheet may abruptlyrise upstream of the downstream end of the guide member to disturb theunfixed toner image on the sheet material.

In an attempt to remove the foregoing inconvenience, Japanese Laid-OpenUtility Model Publication No. 66947/1978, for example, proposes a fixingdevice in which a notch or a depressed portion is formed centrally inthe downstream end of a guide member for guiding a sheet material to apair of fixing rollers so that the central portion of the sheet materialcarried between the fixing rollers can sag down. Elsewhere, JapaneseLaid-Open Utility Model Publication No. 3558/1981 proposes a fixingdevice in which a guide portion for conducting a sheet material havingrelatively high stiffness to the nipping position of a pair of fixingrollers is provided in a guide member for guiding a sheet material tothe fixing rollers.

In the fixing devices disclosed in the specifications of JapaneseLaid-Open Utility Model Publications Nos. 66947/1978 and 3558/1981, asheet material having a relatively small size and relatively highstiffness can be conveyed to near the nip position of the pair of fixingrollers, and the toner image can be fixed on it well. But a sheetmaterial having a relatively small size and relatively low stiffness isnot bent at the downstream end of the guide member and creases arelikely to form on the sheet material during fixing by the pair of fixingrollers.

The fixing device constructed in accordance with the present inventionhas the following improvement in order to remove the aforesaidinconvenience.

With reference to FIGS. 12 to 14, the fixing device improved inaccordance with this invention will be described below in detail.

With reference to FIG. 12, the fixing device 130 has a fixing rollerpair composed of an upper roller 136 and a lower roller 138 cooperatingwith each other. In the illustrated embodiment, the upper roller 136 tobe driven in the direction of an arrow 403 is constructed of acylindrical sleeve member 402 made of aluminum having a surface coatedwith "Teflon" (a tradename for polytetrafluoroethylene made by E. I. duPont de Nemours & Co.), and the lower roller 138 is constructed of ametallic pipe member 404 surface-coated with rubber, etc. Within theupper roller 136 is disposed an electrical heating element 406 such asan electric heater for fixing the toner image on the sheet materialunder heat.

Upstream of the fixing roller pair is disposed a guide member 408 forconducting a sheet material conveyed by the action of the conveyer beltmechanism 128 to the fixing roller pair. As shown in FIG. 13, the guidemember 408 has a main guide 410 formed of a rigid material such as ametallic material and a guide 412 made of a flexible material. The mainguide 410 has a securing portion 410a (constituting the securing portionof the guide member 408) and a guiding portion 410b extending from thesecuring portion 410a. A rectangular cut having a predetermined width isprovided in the central part of the guiding portion 410b in thewidthwise direction (the direction perpendicular to the sheet surface inFIG. 12 and the direction from left bottom to the right top in FIG. 13)(more specifically, the cut is formed from the upstream end to thedownstream end of the guiding portion 410). The guide 412 is disposed inthe aforesaid cut by fixing its upstream end to the securing portion410a of the main guide 410. Thus, the guide 412 and the guiding portion410b of the main guide 410 constitutes the guiding portion of the guidemember 408, and the guide 412 defines a specified area of the guidingportion of the guide member 408. Preferably, the upper surface of theguide 412 is disposed in the same plane as the upper surface of theguiding portion 410b of the main guide 410. Preferably, the guide 412 ofa flexible material is a polyester film having a thickness of about 0.1mm (for example, those commercially available under the tradenames"Lumilar" and "Mylar"). In the illustrated embodiment, a sheet materialhaving relatively high stiffness is assumed to be an official post card,and the width of the aforesaid specified area is set at about 100 mm(substantially equal to, or slightly larger than, the width of theofficial post card).

The guide member 408 consisting of the main guide 410 and the guide 412is fixed to a supporting vertical wall provided in the bottom wallportion 14 which defines the bottom surface of the housing 2 (FIG. 1).As is clear from FIG. 12, the guiding portion of the guide member 408extends upwardly inclinedly toward the downstream side (morespecifically, toward the downstream side in the conveying direction ofthe sheet material shown by an arrow 414), and its lower end portion ispositioned slightly above the nip position of the fixing roller pair(the upper roller 136 and the lower roller 138) and in proximity to theperipheral surface of the upper roller 136. The upstream end (that endwhich is in proximity to the conveying belt mechanism 128) of theguiding portion of the guide member 408 is positioned below the nipposition of the fixing roller pair.

The illustrated conveying belt mechanism 128 includes a pair of rollers416 (FIG. 1) and an endless conveying belt 418 having a plurality ofholes formed therein. The conveyor belt 418 is stretched across therollers 416, and a suction chamber 420 is disposed between the upperportion (the portion acting for conveying the sheet material) and thelower portion of the conveyor belt 418. That surface of the suctionchamber 420 which faces the upper portion of the conveyor belt 418 isopened. The inside of the suction chamber 420 is sucked by a suctionmotor (not shown), and by the sucking action of the suction motor, thesheet material conveyed on the upper portion of the conveyor belt 418 isattracted to the conveyor belt 418.

In the fixing device 130 described above, the sheet material having atoner image on its upper surface which is conveyed on the conveyor belt418 is conducted to the fixing roller pair by being guided by the uppersurface of the guiding portion of the guide member 408. By the fixingaction of the fixing roller pair, the toner image is fixed to thesurface of the sheet material.

The operation and advantage of the fixing device 130 including the guidemember 408 described above will be described with reference to FIGS. 12to 14.

Let us first assume that a sheet material having a relatively largewidth (more specifically larger than the width of the aforesaidspecified area in the transverse direction) is used. As can be easilyunderstood from FIG. 13, the sheet material is raised while being guidedmainly by the upper surface of the guiding portion 410b of the mainguide 410 of the guide member 408, and thereafter, lowered and conductedto the nip position of the fixing roller pair (the upper roller 136 andthe lower roller 138). Accordingly, the sheet material is conveyed asshown by a two-dot chain line in FIG. 12 and bent by the downstream endof the guiding portion 410b of the main guide 410. Creases will bestraightened by this bending action. As a result, the sheet material canbe introduced between the fixing rollers after its creases have beenremoved, and the occurrence of creases in the sheet material during thefixing operation can be prevented.

Now, let us assume that a sheet material having a relatively small width(more specifically smaller than the width of the aforesaid specifiedarea in the transverse direction) and relatively high stiffness(generally sheet materials having relatively high stiffness mostly havea large weight), for example, an official post card, is used. As can bereadily understood from FIG. 13, the sheet material is conducted to thenip position of the fixing roller pair by being guided by the uppersurface of the guide 412 (the specified area). When the sheet materialis guided over the upper surface of the guide 412, the downstream endportion of the guide 412 is bent downwardly by the weight of the sheetmaterial as shown in FIG. 14 because the guide 412 is made of a flexiblematerial. Thus, the downstream end of the guide 412 is at nearly thesame height as the nip position of the fixing roller pair. Accordingly,the sheet material is conveyed as shown by a two-dot chain line in FIG.14 and conveyed to the nip position of the fixing roller pair nearly ina straight line fashion without being bent by the downstream end of theguide 412. Thus, sheet jamming and disturbance of the unfixed tonerimage, which may occur when a sheet material having relatively highstiffness is used, can be prevented.

Now, let us assume that a sheet material having a relatively small width(more specifically, smaller than the width of the specified area in thetransverse direction) and relatively low stiffness (generally sheetmaterials having relatively low stiffness have a small weight) is used.The sheet material in this case is brought to the nip position of thefixing roller pair while being guided by the upper surface of the guide412 (specified area). But since its weight is small, the downstream endportion of the guide 412 is not so much bent downwardly when the sheetmaterial is guided over the upper surface of the guide 412. The sheetmaterial is raised by being guided by the upper surface of the guide 412and then lowered and conducted to the nip position of the fixing rollerpair. Accordingly, the sheet material is conveyed as shown by a two-dotchain line in FIG. 12 and bent by the downstream end of the guide 412.Creases in the sheet material will be straightened by this bendingaction. In this case, too, the sheet material can be passed between thefixing rollers after its creases have been removed.

In the embodiment described above, the guide 412 (specified area) isdisposed in the central portion of the guiding portion of the guidemember 408 in the widthwise direction. When a sheet material having arelatively small size is to be guided on the upper surface of the leftside portion (or the right side portion) in the widthwise direction ofthe guiding portion of the guide member 408, the guide 412 may beprovided in the left side portion (or the right side portion) in thewidthwise direction of the guiding portion of the guide member 408.

The above embodiment is applied to a fixing device including anelectrical heating element. It can, however, be also applied to a fixingdevice of the pressure type which is adapted to fix the toner image onthe sheet material only by the pressure between the fixing rollers.

Controlling of the Fixing Device Based on Temperature

In an electrostatic copying apparatus having a fixing device equippedwith an electrical heating element such as an electric heater, the typedescribed hereinabove, varuous improvements have been suggested forsaving power consumption. For example, Japanese Laid-Open PatentPublication No. 92558/1981 discloses an electrostatic copying apparatusincluding a timer circuit which starts its operation when thetemperature of an electrical heating element reaches a predeterminedtemperature after closing a power supply switch or when the copyingcycle has ended, and generates a signal when the above operationcontinued for a preset period of time; a reset means for resetting thetimer circuit when a copying cycle signal is generated within the periodof time preset in the timer circuit; and a current shutting means forshutting the passing of an electric current to the electrical heatingelement when the signal is outputted from the timer circuit. In theelectrostatic copying apparatus disclosed in this patent document, thetimer circuit operates when the temperature of the electrical heatingelement reaches a predetermined point after closing the power supplyswitch or the copying cycle has ended. When thereafter no copying cyclesignal is gnerated within a predetermined period of time, a signal isoutputted by the timer circuit to cut off the passing of a current tothe electrical heating element. Thus, after the lapse of a predeterminedperiod of time from the operation of the timer circuit, powerconsumption by the electrical heating element is prevented.

In the above electrostatic copying apparatus, when a predeterminedperiod of time elapses without resetting after the actuation of thetimer circuit, the passing of an electric current to the electricalheating element is shut off. On the other hand, when a copying cyclesignal is generated within the predetermined period of time after theactuation of the timer circuit, the timer circuit is reset, and theelectrical heating element continues to be maintained at a predeterminedtemperature. Accordingly, the power consumption by the electricalheating element is not sufficiently reduced, and it is still desired toreduce power consumption more effectively without affecting the fixingoperation.

To solve the aforesaid problem, the electrostatic copying apparatushaving the fixing device equipped with the electrical heating elementconstructed in accordance with this invention is improved in thefollowing respect.

With reference to FIGS. 15 to 17, the electrostatic copying apparatusincluding the fixing device 130 with the electrical heating element 406comprises a temperature detecting means for detecting the temperature ofthe fixing device 130 at a predetermined position. In the illustratedembodiment, the temperature detecting means is comprised of a thermistor430 whose resistance value decreases with an increase in temperature. Asshown in FIG. 12, the thermistor 430 is provided in proximity to theperipheral surface of the upper roller 136 of the fixing roller pair(and therefore, the thermistor 430 detects the temperature of thesurface of the upper roller 136 or its vicinity). With reference to FIG.15, one terminal of the thermistor 430 is connected to a power supply Evia a resistance R₁, and the other terminal is connected to one inputterminal of each of a first comparator 432 and a second comparator 434.One terminal each of a resistance R₂ and a condenser C disposed parallelto each other is connected to the connecting portion between the otherterminal of the thermistor 430 and the one input terminal of the firstcomparator 432 and the one input terminal of the second comparator 434.The other terminals of the resistance R₂ and condenser C arerespectively grounded. A circuit portion including resistances R₃, R₄and R₅ connected to each other in series is disposed parallel to theaforesaid circuit portion including the resistance R₁, the thermistor430, the resistance R₂ and the condenser C. One end of the circuitportion (one terminal of the resistance R₃) is connected to a powersupply E, and the other terminal (one terminal of the resistance R₅) isgrounded. The connecting portion between the resistances R₃ and R₄ isconnected to the other input terminal of the first comparator 432, andthe connecting portion between the resistances R₄ and R₅ is connected tothe other input terminal of the second comparator 434. Accordingly, thevoltage of the other terminal of the thermistor 430 is applied to oneinput terminal of the first comparator 432, and the voltage of theconnecting portion between the resistances R₃ and R₄ (a first referencevoltage) is applied to the other input terminal of the first comparator432. The first comparator 432 produces a signal "H" when the voltage ofthe other terminal of the termistor 430 becomes lower than the voltageof the connecting portion between the resistances R₃ and R₄. The voltageof the other terminal of the thermistor 430 is applied to one inputterminal of the second comparator 434, and the voltage (a secondreference voltage) of the connecting portion between the resistances R₄and R₅ is applied to the other input terminal of the second comparator434. The second comparator 434 generates a signal "H" when the voltageof the other terminal of the thermistor 430 becomes lower than thevoltage of the connecting portion between the resistances R₄ and R₅. Thevoltage of the connecting portion between the resistances R₃ and R₄ andthe voltage of the connecting portion between the resistances R₄ and R₅,i.e. the first and second reference voltages, can be set at desiredvalues by properly selecting the resistance values of the resistancesR₃, R₄ and R₅. In the illustrated embodiment, the first referencevoltage is set so that it becomes equal to the voltage of the otherterminal of the thermistor 430 (and therefore the voltage applied to oneinput terminal of the first comparator) at which the temperaturedetected by the termistor 430 is a first predetermined temperature T₁(for example, about 185° C.) suitable for fixation. The second referencevoltage is set so that it becomes equal to the voltage of the otherterminal of the thermistor 430 (and therefore the voltage applied to oneinput terminal of the second comparator 434) at which the temperaturedetected by the thermistor 430 is a second predetermined temperature T₂which does not adversely affect the fixing operation even when thecopying cycle is started. Accordingly, when the temperature detected bythe thermistor 430 (i.e. the temperature of the surface of the upperroller 136 or its vicinity) is lower than the first predeterminedtemperature T₁, the first comparator 432 generates a signal "H". Whenthe temperature detected by the thermistor 430 is lower than the secondpredetermined temperature T₂, the second comparator 434 generates asignal "H".

The output signals from the first comparator 432 and the secondcomparator 434 are fed into the aforesaid control means 250 which maypreferably be constructed of a microprocessor. A copying cycle signalfrom a copying cycle signal producing means 438 is also fed to thecontrol means 250. The copying cycle signal producing means 438 isconstructed, for example, of a signal producing means which produces acopying cycle signal until the copying cycle has been performed througha preset number of cycles after depression of a copying start switch(not shown). The copying cycle signal producing means 438 may also beadapted to start generation of a copying cycle signal in response not tothe closing of the copying start switch but to an operation carried outprior to the starting of the copying cycle, for example, to theoperation of a setting key for presetting the number of copies to beproduced. Alternatively, the signal producing means 438 may be adaptedto produce a copying cycle signal without fail for a predetermined timeupon closing of the power supply switch.

On the other hand, in the control means 250, an actuation signal forenergizing the electrical heating element 406 (FIG. 12) in relation tothe signal "H" from the first comparator 432 is produced in the controlmeans 250, and a power supply shutting signal for opening the powersupply switch 440 of the electrostatic copying apparatus in relation tothe signal "H" from the second comparator 434 is also generated. Theactuation signal is fed to a switch means 442 disposed in a circuit forsupplying an electrical current to the electrical heating element 406,and the power supply shutting signal, to the power supply switch 440.The control means 250 illustrated is constructed such that it continuesto produce the actuation signal after the closing of the power supplyswitch 440 until the temperature detected by the thermistor 430 exceedsthe first predetermined temperature T₁.

With reference to FIGS. 15 and 16, the controlling of the fixing devicein the aforesaid electrostatic copying apparatus on the basis oftemperature will be described.

When the power supply switch 440 is closed, the control means 250produces an actuation signal which is then fed into the switch means442. As a result, the switch means 442 is closed, and an electriccurrent is passed through the electrical heating element 406 via theswitch means 442. As a result, the fixing device 130 is heated by theelectrical heating element 406 until the temperature detected by thethermistor 430 reaches the first predetermined temperature T₁ (about185° C., for example). Hence, when the power supply switch 440 is closedat time t_(o), the fixing device 130 is heated by the passing of acurrent through the electrical heating element 406, and the temperaturedetected by the thermistor 430 is raised as shown by a solid line inFIG. 16. After the lapse of time t_(o1) from the time t_(o), thetemperature detected by the thermistor 430 reaches the firstpredetermined temperature T₁.

When the temperature detected by the thermistor 430 reaches the firstpredetermined temperature T₁, the voltage of the other terminal of thethermistor (and therefore the voltage applied to one input terminal ofthe first comparator 432) becomes higher than the voltage of theconnecting portion between the resistances R₃ and R₄ (and therefore thevoltage applied to the other input terminal of the first comparator432), and the feeding of the signal "H" from the first comparator 432 isstopped. As a result, the supplying of the actuation signal to theswitch means 442 is stoped, and the switch means 442 is opened to cancelthe passing of an electrical current to the electrical heating element406. Once the temperature detected by the thermistor 430 has reached thefirst predetermined temperature T₁ (the arrival at the firstpredetermined temperature T₁ can be detected by the stopping of thesupplying of the signal "H" from the first comparator 432), theelectrical heating element 406 is controlled depending upon whether thecopying cycle signal producing means 438 produces a copying cyclesignal. When the signal producing means 438 is producing a copying cyclesignal, the electrical heating element 406 is controlled by the outputsignal from the first comparator 432, and consequently, the electricalheating element 406 is controlled so that the temperature detected bythe thermistor 430 becomes substantially equal to the firstpredetermined temperature T₁. (More specifically, when the means 438 isproducing the copying cycle signal, the control means 250 produces anactuation signal on the basis of the signal "H" from the firstcomparator 432. This actuation signal closes the switch means 442 andenergizes the electrical heating element 406. Furthermore, the feedingof the actuation signal is stopped by the stopping of the feeding of thesignal "H" from the first comparator 432. This opens the switch means442 and deenergizes the electrical heating element 406. Thus, theelectrical heating element is controlled as stated above.) On the otherhand, when the means 438 is not producing the copying cycle signal, thefeeding of the actuation signal from the control means 250 is stoppedowing to the absence of the copying cycle signal irrespective of theoutput signals from the first comparator 432 and the second comparator434, and the switch means 442 is opened to deenergize the electricalheating element. Accordingly, when the copying cycle signal is producedafter the temperature detected by the thermistor 430 has exceeded thefirst predetermined temperature T₁, the temperature detected by thethermistor 430 is controlled substantially to the first predeterminedtemperature T₁ as shown by the solid line in FIG. 16. When thereafterthe feeding of the copying cycle signal is stopped at time t₁, theelectrical heating element 406 is deenergized and the temperaturedetected by the thermistor 430 is lowered as shown by a two-dot chainline in FIG. 16 after time t₁.

When the electrical heating element 406 is deenergized and thetemperature detected by the thermistor 430 becomes lower than the secondpredetermined temperature T₂ (about 150° C., for example), the voltageof the other terminal of the thermistor 430 (and therefore the voltageapplied to one input terminal of the second comparator 434) becomeslower than the voltage of the connecting portion between the resistancesR₄ and R₅ (and therefore the voltage applied to the other input terminalof the second comparator 434), and a signal "H" is fed from the secondcomparator 434. On the basis of this signal "H", the control means 250produces a power supply shutting signal which causes opening of thepower supply switch 440 (and therefore the feeding of an electriccurrent to the electrostatic copying apparatus is stopped). When afterstopping of the feeding of the copying cycle signal at time t₁, themeans 438 produces a copying cycle signal (produced, for example, bydepressing the copying start switch) at time t₂ (at which thetemperature detected by the thermistor 430 has not been lowered to thesecond predetermined temperature T₂), the electrical heating element 406is controlled on the basis of the output signal from the firstcomparator 432, and the temperature detected by the thermistro 430 israised as shown by a one-dot chain line in FIG. 16 after time t₂, andthereafter, the detected temperature becomes substantially equal to thefirst predetermined temperature T₁ as shown by the solid line in FIG.16. When, for example, the copying start switch (not shown) is depressedat time t₃ or later after the stopping of the feeding of the copyingcycle signal at time t₁, the electrical heating element 406 will not beenergized since the power supply switch 440 is off.

When the production of a copying cycle signal is again terminated attime t₄ after the production of the copying cycle signal at time t₂, thefeeding of the actuation signal from the control means 250 is stopped,and the switch means 442 is turned off to deenergize the electricalheating element 406. Accordingly, when the production of the copyingcycle signal is again terminated at time t₄, the electrical heatingelement 406 is deenergized and the temperature of the thermistor 430detected is lowered as shown by the solid line in FIG. 16 after time t₄.When the temperature detected by the thermistor 430 becomes lower thanthe second predetermined temperature T₂ at time t₅, the power supplyswitch 440 is turned off to stop feeding an electric current to theelectrostatic copying apparatus. To start the copying cycle after thepower supply switch 440 has been turned off in this manner, the powersupply switch 440 is again closed. As a result, the electrostaticcopying apparatus is controlled as stated above.

The electrostatic copying apparatus equipped with the fixing device 130including the electrical heating element 406 is constructed such thatthe electrical heating element is deenergized when after the temperaturedetected by the thermistor 430 has exceeded the first predeterminedtemperature T₁, a copying cycle signal is not produced. Accordingly,wasteful consumption of power by the electrical heating element 406 canbe prevented, and the power can be saved more effectively than in theprior art.

Furthermore, the aforesaid fixing device 130 is constructed such thatthe power supply switch is turned off when the electrical heatingelement 406 is deenergized and the temperature detected by thethermistor 430 (i.e. the temperature of the surface of the upper roller136 and its vicinity) is lowered to the second predetermined temperatureT₂. Hence, it is possible to prevent surely the performance of thefixing operation at a temperature below the second predeterminedtemperature T₂ (the temperature at which fixation is not adverselyaffected even when the copying cycle is started), and poor fixation canbe prevented.

Controlling of the passing of an electric current to the electricalheating element 406 during the generation of the copying cycle signal isnot limited to the opening or closing of the switch means 442 by theactuation signal. Alternatively, the number of half cycles of analternate current fed to the electrical heating element 406 can becontrolled on the basis of the output signal from the thermistor 430, orthe conducting phase angle of each half cycle of an alternate currentfed to the electrical heating element may also be controlled in order toachieve the above purpose.

The above specific embodiment is constructed such that when no copyingcycle signal is produced after the temperature detected by thethermistor 430 has exceeded the first predetermined temperature T₁, theelectrical heating element 406 is deenergized, and when the temperaturedetected by the thermistor becomes lower than the second predeterminedtemperature T₂, the power supply switch 442 is opened. Alternatively, itis also possible to construct it such that when no copying cycle signalis produced after the detected temperature has exceeded the firstpredetermined temperature T₁, the electrical heating element 406 isdeenergized, and when the detected temperature is lowered to the secondpredetermined temperature T₂, it is maintained at the secondpredetermined temperature T₂. This alternative means can also lead tothe effective saving of power.

Now, with reference to FIG. 17, the operation and advantage of the abovemodified embodiment will be briefly described. The control circuit inthe modified embodiment is substantially the same as the control circuitof the embodiment shown in FIG. 15 except that the power supply switch440 is excluded. A description of the structure of the control circuititself is omitted, but the same parts will be referred to by the samereference numerals. When the power switch 440 is closed at time t_(o),an actuation signal is generated in the control means 250, and thisactuation signal continues to be generated until the temperaturedetected by the thermistor 430 has exceeded the first predeterminedtemperature T₁ (about 185° C.). As a result, the switch means 442 isclosed, and the electrical heating element 406 conducts via the switchmeans 442, and the temperature detected by the thermistor 430 is raisedto the first predetermined temperature T₁. When after the lapse of timet_(o1) from the closing of the power supply switch 440 the detectedtemperature of the thermistor 430 exceeds the first predeterminedtemperature T₁, the electrical heating element 406 is thereaftercontrolled depending upon whether the copying cycle signal producingmeans 438 is producing a copying cycle signal or not. When the copyingcycle signal is produced even after the detected temperature has reachedthe first predetermined temperature T₁, the electrical heating element406 is controlled on the basis of the output signal from the firstcomparator 432. Thus, the electrical heating element 406 is controlledso that the detected temperature of the thermistro 430 becomessubstantially equal to the first predetermined temperature T₁. On theother hand, when at time t₁, the production of the copying cycle signalis terminated, the electrical heating element 406 is controlled on thebasis of the output signal from the second comparator 434. Thus, theelectrical heating element 406 is deenergized until time t₂, andthereafter, controlled so that the temperature detected by thethermistro 430 becomes substantially equal to the second predeterminedtemperature T₂.

When a copying cycle signal is again produced (for example, bydepressing the copying start switch), the electrically heating element406 is controlled on the basis of the output signal from the firstcomparator 432. Thus, the electrical heating element 406 is energizeduntil time t₄ and thereafter controlled again such that the temperaturedetected by the thermistor 430 becomes substantially equal to the firstpredetermined temperature T₁.

When thereafter the generation of the copying cycle signal is terminatedat time t₅ and the power supply switch 442 is opened at time t₇, feedingof an electrical current to the electrostatic copying apparatus isstopped, whereby the electrical heating element 406 is not energized andthe temperature detected by the thermistor 430 is lowered.

ACTUATION CONTROL

Controlling of the actuation of the copying apparatus described abovewill be described in summary.

With reference to FIG. 1, sheet material detecting switches S1 and S2are disposed in the sheet material conveying passage. The detectingswitch S1 has a detecting arm which slightly upstream of the pair ofconveyor rollers 120 and 122, crosses the sheet material conveyingpassage between the guide plates 114 and 116 and also the sheet materialconveying passage between the guide plates 114 and 118. It detects asheet material fed from the paper feeding device 90 and passing betweenthe guide plates 114 and 116 and also a sheet material fed from themanual feeding device 92 and passing between the guide plates 114 and118. The detecting switch S2 has an arm which slightly upstream of thepair of feed rollers 110 and 112, crosses a conveying passage for asheet material inserted between the guide plates 106 and 108, anddetects a sheet material positioned on the guide plate 106 and advancedby hand.

With reference to FIGS. 18 and 19 taken in conjunction with FIG. 2,document placing mean detecting switches S3 and S4 are disposed belowthe supporting base plate 50 of the document placing means 48. Actuationpieces 502, 504 and 506 are fixed to the lower surface of the supportingbase plate 50. When the document placing means 48 is held at thestart-of-scan position shown by the two-dot chain line 48A in FIG. 1,the actuation piece 502 acts on the detecting switch S3 to close it.When the document placing means 48 is moved for scanning exposure by apredetermined distance to the right in FIGS. 1, 18 and 19, the actuatingpiece 504 acts on the detecting switch S4 to close it. When the documentplacing means 48 continues to make a scanning exposure movement and isheld at the scan exposure movement limit position shown by the two-dotchain line 48B in FIG. 1, the actuating piece 506 acts on the detectingswitch S4 to close it (thus, the document placing means 48 is surelyprevented from moving to the right in FIG. 1 beyond the scanningexposure movement limit position shown by the two-dot chain line 48B inFIG. 1).

Furthermore, in the illustrated embodiment, there is provided a drivingamount detecting means for detecting the amount of a rotating elementwhich is always rotated when the driving source 144 (FIG. 3) isenergized. With reference to FIGS. 20 and 21, a detection plate 510 andthe gear 206 already referred to with reference to FIG. 3 are fixed to ashaft 508 to which the feed roller 112 (FIG. 1) is secured. A pluralityof circumferentially spaced cuts 512 are formed in the peripheral edgeportion of the detection plate 510. The driving amount detecting meansis comprised of an optical detector 518 having a light emitting element514 located on one side of the peripheral edge portion of the detectionplate 510 and a light receiving element 516 located on the other side.The detector 518 generates a pulse signal every time the cut 512 ispositioned between the light emitting element 514 and the lightreceiving element 516 during the rotation of the detection plate 510,and thereby the light receiving element 516 receives the light from thelight emitting element 514 or the detection plate 510 shuts off thelight from the light emitting element.

With reference to FIG. 22, the detecting signals produced by the variousdetecting swtiches and detectors described above are fed into thecontrol means 250 which may be a microprocessor, and the control means250 controls the actuations of the various means of the copyingapparatus according to the signals fed thereinto.

With reference to FIGS. 23-A and 23-B, the modes of controlling thevarious means of the copying apparatus will be described. In step n1,the copying start switch PS is closed to start a copying cycle. Thisresults in energization of the driving source 144 in step n2,energization of the peeling corona discharge device 76 in step n3,lighting of the charge eliminating lamp 82 in step n4, and actuation ofthe clutch means 174 for reverse motion in the power transmissionmechanism 166 in step n5. As a result, the document placing means 48starts its preparatory movement from its stop position shown by thesolid line in FIG. 1 to the left in FIG. 1 at a speed 2 V. Every timethe detector 518 generates a pulse signal, a first counter means C1built in the control means 250 subtracts 2 from the cumulative count instep n6 (as will be made clear from the following description, when thedocument placing means 48 starts to make a preparatory movement from itsstop position, the first counter means C1 has a predetermined count).Then, in step n7, it is judged whether or not the detecting switch S3 isclosed, and therefore whether the document placing means 48 has made apreparatory movement to the start-of-scan position shown by the two-dotchain line 48A in FIG. 1. When the detecting switch S3 is closed, stepn8 sets in, and the clutch means 174 for reverse motion in the powertransmission mechanism 166 for the document placing means 48 is renderedinoperative. Thus, the document placing means 48 is stopped at thestart-of-scan position shown by the two-dot chain line 48A in FIG. 1. Instep n9, the first counter means C1 stops subtraction from thecumulative count (at this time, the count of the first counter means C1becomes zero unless errors have been accumulated). In step n10, a feedclutch means CL1 for connecting the feed roller 94 of the paper feeddevice 90 to the driving source 144 is actuated, and the feeding of acopying paper sheet from the paper cassette 100 is started. In step n11,the document illuminating lamp 84 is turned on. In step n12, a secondcounter means C2 built in the control means 250 starts to count thepulse signals generated by the detector 518. In step n13, it is judgedwhether or not the detecting switch S1 has been closed and therefore theleading edge of the sheet material fed from the copying paper cassette100 has reached the detecting arm of the detecting switch S1. When thedetecting switch S1 has been closed, step n14 sets in, and a thirdcounter means C3 in the control means 250 starts to count the pulsesignals generated by the detector 518. Then, in step n15, it is judgedwhether or not the third counter means C3 has counted a predeterminedvalue. This predetermined value corresponds to the time which isrequired for the leading edge of the sheet material to reach the nipposition of the conveyor rollers 120 and 122 after its arrival at thedetecting arm of the detecting switch S1. When the third counter meansC3 has counted the predetermined value, step n16 sets in, and the feedclutch means CL1 is rendered inoperative. Then, in step n17, it isjudged whether or not the second counter means C2 which started countingin step n12 has counted a predetermined value. This predetermined valuecorresponds to the time required for the document illuminating lamp 84turned on in step n11 to assume a stable state. When the second countermeans C2 has counted the predetermined value, step n18 sets in, and thecharging corona discharge device 68 is energized. In step n19, a fourthcounter means C4 built in the control means 250 starts to count thepulse signals generated by the detector 518. Then, in step n20, it isjudged whether or not the fourth counter means C4 has counted apredetermined value. This predetermined value corresponds to the sum ofthe time required for the charging corona discharge device 68 energizedin step n18 to assume a stable state and the time required for aspecified position of the photosensitive member on the rotating drum 64to move by the rotation of the rotating drum 64 from a position at whichit undergoes the action of the corona discharge device 68 to a positionat which it is exposed through the optical unit 70. When the fourthcounter means C4 has counted a predetermined value, step n21 sets in,and the count of the first counter means C1 is returned to zero if it isnot zero owing to the accumulation of errors. In step n22, the clutchmeans 172 for normal motion in the power transmission mechanism 166 forthe document placing means 48 is actuated, and the document placingmeans 48 starts to make a scanning exposure movement at a speed V to theright in FIG. 1 from its start-of-scan position shown by the two-dotchain line 48A in FIG. 1. In step n23, the first counter means C1 beginsto add one to the cumulative count every time the detector 518 producesa pulse signal. Then, in step n24, it is judged whether or not thedetecting switch S4 has been closed, and the document placing means 48has been moved a predetermined distance to the right in FIG. 1 from thestart-of-scan position shown by the two-dot chain line 48A in FIG. 1.When the detecting switch S4 has been closed, step n25 sets in, and aconveying clutch means CL2 for connecting the conveyor roller 122 to thedriving source 114 is actuated, and consequently, conveying of the sheetmaterial whose leading edge is at a stop while being in abutment againstthe nip position of the conveyor rollers 120 and 122 is started. In stepn26, a fifth counter means C5 built in the control means 250 begins tocount the pulse signals generated by the detector 518. Then, in stepn27, it is judged whether or not the fifth counter means C5 has counteda predetermined value. This predetermined value corresponds to the timerequired for the leading edge of the sheet material whose conveying wasstarted in step n26 to reach a position at which it undergoes the actionof the transferring corona discharge device 74. When the fifth countermeans C5 has counted the predetermined value, step n28 sets in, and thetransferring corona discharge device 74 is energized. Then, in step n29,it is judged whether or not the detecting switch S1 has been opened andtherefore whether the trailing edge of the sheet material has gone pastthe detecting arm of the detecting switch S1. When the detecting switchS1 has been opened, step n30 sets in, and the clutch means 172 of thepower transmission mechanism 166 is rendered inoperative, and thescanning exposure movement of the document placing means 48 isterminated corresponding to the length of the sheet material. In stepn31, the first counter means C1 stops making additions to the count. Instep n32, the charging corona discharge device 68 is deenergized. Instep n33, a sixth counter means C6 built in the control means 250 startsto count the pulse signals generated by the detector 518, and in stepn34, a seventh counter means C7 built in the control means 250 begins tocount the pulse signals generated by the detector 518. Then, in stepn35, it is judged whether or not the sixth counter means C6 has counteda predetermined value. This predetermined value corresponds to the timerequired for the trailing edge of the sheet material to go past theposition at which it undergoes the action of the corona discharge device74, after going past the detecting arm of the detecting switch S1. Whenthe sixth counter means C6 has counted the predetermined value, step n36sets in, and the corona discharge device 74 is deenergized. In step n37,the conveying clutch means CL2 is rendered inoperative. Then, step n38sets in, and it is judged whether or not the seventh counter means C7has counted a predetermined value. This predetermined value correspondsto the time interval which is desired so as to prevent vibration, etc.during the time period which runs from the time of rendering the clutchmeans 172 inoperative to the time of rendering the clutch means 174operative. When the seventh counter means C7 has counted thepredetermined value, step n39 sets in, and the document illuminatinglamp 84 is turned off. In step n40, the clutch means 174 for reversemotion in the power transmission means 166 is actuated, andconsequently, the document placing means 48 begins to make a returningmovement at a speed 2 V to the left in FIG. 1. Then, in step n41, it isjudged whether or not the copying cycle should be performed repeatedly.When the copying step is to be repeated, one goes back to step n6. Whenthe copying cycle should not be repeated, step n 42 sets in, and thefirst counter means C1 begins to subtract 2 from the cumulative countevery time the detector 518 produces a pulse signal. Then in step n43,it is judged whether or not the count of the first counter means C1 hasbeen subtracted to a predetermined value. This predetermined valuecorresponds to the distance of movement between the stop position of thedocument placing means 48 shown by the solid line in FIG. 1 and itsstart-of-scan position shown by the two-dot chain line 48A in FIG. 1.When the count of the first counter means C1 has been subtracted to thepredetermined value, step n44 sets in, and the clutch means 174 forreverse motion in the power transmission mechanism 166 is renderedinopeative. Thus, the document placing means 48 can be stopped at thestop position with a sufficient accuracy without the need for adetecting switch for detecting the occupation of the stop position bythe document placing means 48. In step n45, the first counter means C1stops subtraction. In step n46, an eighth counter means C8 built in thecontrol means 250 starts to count the pulse signals generated by thedetector 518. Then, in step n47, it is judged whether or not the eighthcounter means C8 has counted a predetermined value. This predeterminedvalue may correspond to the time required for the rotating drum 64 torotate further through about one turn after the transferring operation.When the eighth counter means C8 has counted the predetermined value,step n48 sets in, and the driving source 144 is deenergized. In stepn49, the peeling corona discharge device 76 is deenergized, and in stepn50, the charge eliminating lamp 82 is turned off.

The aforesaid controlling mode is applicable when the sheet material isautomatically fed from the copying paper feed device 90. When the sheetmaterial is to be inserted manually to the manual feed device 92, thecontrolling mode differs in the following respects. Firstly, in step n1,instead of judging whether or not the copying start switch PS is closed,it is judged whether or not the detecting switch S2 has been closed andtherefore the leading edge of the sheet material inserted manually hasarrived at the detecting arm of the detecting switch S2. Secondly, stepsn10, n14, n15 and n16 are omitted. Otherwise, the controlling mode issubstantially the same as that described hereinabove. The feed rollers110 and 112 of the manual feed device 92 are kept rotating even afterthe leading edge of the sheet material fed by it is stopped while beingin abutment against the nip position of the conveyor rollers 120 and122. Since, however, the feed roller 110 is pressed relatively lightlyagainst the feed roller 112 by its own weight, the feed rollers 110 and112 slip with respect to the sheet material when it is stopped with itsleading edge in abutment against the aforesaid nip position. Thus, thefeed rollers 110 and 112 do not adversely affect the sheet material.

The electrostatic copying apparatus improved in accordance with thisinvention has been described in detail hereinabove with reference to itspreferred embodiments shown in the accompanying drawings. It should beunderstood however that the invention is is not limited to thesespecific embodiments, and various changes and modifications are possiblewithout departing from the scope of the invention.

What we claim is:
 1. An electrostatic copying apparatus comprising adocument placing means being reciprocally mounted and having atransparent plate for placing a document thereon, a driving source, apower transmission mechanism including a clutch means for normal motionand a clutch means for reverse motion for drivingly coupling the drivingsource to the document placing means, a driving amount detecting meansfor detecting the amount of rotation of a rotating element adapted to berotated when the driving source is energized, and a control means foractuating the clutch means for normal motion to move the documentplacing means for scanning exposure in a predetermined direction from apredetermined start-of-scan position in a copying cycle, and renders theclutch means for normal motion and simultaneously with it or after it,actuates the clutch means for reverse motion to move the documentplacing means in the reverse direction; wherein said control meansrenders the clutch means for reverse motion inoperative, and therebystops the document placing means at a predetermined stop opposition,when the amount of rotation of the rotating element during the scanningexposure movement of the document placing means is in a predeterminedrelation to the amount of rotation of the rotating element after thestarting of the returning movement of the document placing means.
 2. Theapparatus of claim 1 wherein the control means at the time of thecopying cycle first actuates the clutch means for reverse motion tocause the document placing means to make a preparatory movement fromsaid stop position in the reverse direction, and when the documentplacing means has made a preparatory movement to the start-of-scanposition, the control means renders the clutch means for reverse motioninoperative.
 3. The apparatus of claim 1 wherein the control meansrenders the clutch means for normal motion inoperative when the documentplacing means has made a scanning exposure movement over a distancecorresponding to the length of a copying paper in said predetermineddirection from said start-of-scan position.
 4. The apparatus of claim 1wherein the rotating element is a detection plate having a plurality ofcircumferentially spaced cuts formed in its peripheral edge portion; thedriving amount detecting means includes a detector having a lightemitting element located on one side of the peripheral edge portion ofthe detection plate and a light receiving element located on the otherside and produces a pulse signal every time the light receiving elementreceives the light from the light emitting element by the positioning ofthe cut between the light emitting element and the light receivingelement or every time the light from the light emitting element is shutoff by the detection plate; and said control means renders the clutchmeans for reverse motion inoperative when the number of pulse signalsproduced by the driving amount detecting means during the scanningexposure movement of the document placing means is in a predeterminedrelation to the number of pulses produced by the driving amountdetecting means after the document placing means has started to make areturning movement.
 5. The apparatus of claim 4 wherein said controlmeans includes counter means for performing addition every time thedriving amount detecting means produces a pulse signal during thescanning exposure movement of the document placing means and performingsubtraction every time the driving amount detecting means produces apulse signal during the returning movement of the document placingmeans, and when the count of the counter is subtracted to apredetermined value, said control means renders the clutch means forreverse motion inoperative.
 6. The apparatus of claim 5 wherein when theclutch means for normal motion is actuated, the document placing meansis moved in said predetermined direction at a speed V, and when theclutch means for reverse rotation is actuated, the document placingmeans is moved in said reverse direction at a speed 2 V, and saidcounter means adds one to the cumulative count every time the drivingamount detecting means produces a pulse signal during the movement ofthe document placing means in said predetermined direction, andsubtracts 2 from the cumulative count every time the driving amountdetecting means produces a pulse signal during the movement of thedocument placing means in the reverse direction.
 7. The apparatus ofclaim 5 wherein when the document placing means is held at thestart-of-scan position, the counter means is necessarily reset to zero.